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Journal of Clinical Endocrinology & Metabolism , doi:10.1210/jc.2005-2069
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The Journal of Clinical Endocrinology & Metabolism Vol. 91, No. 4 1501-1507
Copyright © 2006 by The Endocrine Society

Free Fatty Acids Increase Androgen Precursors in Vivo

K. Mai, T. Bobbert, V. Kullmann, J. Andres, H. Rochlitz, M. Osterhoff, M. O. Weickert, V. Bähr, M. Möhlig, A. F. H. Pfeiffer, S. Diederich and J. Spranger

Department of Endocrinology, Diabetes and Nutrition (K.M., T.B., V.K., J.A., H.R., M.O., M.O.W., V.B., M.M., A.F.H.P., S.D., J.S.), Charite–University Medicine Berlin, Campus Benjamin Franklin, 12200 Berlin, Germany; Department of Clinical Nutrition (K.M., T.B., V.K., J.A., H.R., M.O., M.O.W., V.B., M.M., A.F.H.P., S.D., J.S.), German Institute of Human Nutrition Potsdam-Rehbrücke, 14558 Nuthetal, Germany; and Endokrinologikum (S.D.), 10117 Berlin, Germany

Address all correspondence and requests for reprints to: Joachim Spranger, M.D., Department of Clinical Nutrition, German Institute of Human Nutrition Potsdam-Rehbrücke, Arthur-Scheunert-Allee 114-116, 14558 Nuthetal, Germany. E-mail: spranger{at}mail.dife.de or joachim.spranger{at}charite.de.


   Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Context: There is considerable evidence that metabolic factors such as insulin resistance may induce hyperandrogenemia in polycystic ovary syndrome. However, other metabolic factors such as free fatty acids (FFAs) may also contribute to androgen excess.

Objective: The objective was to study effects of FFAs on adrenal production of androgen precursors in vivo.

Design and Participants: We investigated eight healthy young men, because male individuals produce the androgen precursors dehydroepiandrosterone (DHEA), DHEA sulfate, and androstenedione predominantly in the adrenal gland. A randomized controlled crossover trial was performed.

Intervention: After a 10-h overnight fast, 20% lipid/heparin or saline/heparin infusion was given at a rate of 1.5 ml/min. Four hours after start of lipid infusion, a euglycemic hyperinsulinemic clamp was performed.

Main Outcome Measures: DHEA, androstenedione, 17-OH-progesterone, testosterone, estrone, LH, FSH, ACTH, and cortisol were measured.

Results: The adrenal androgen precursors DHEA and androstenedione showed a circadian decline during saline/heparin infusion (P < 0.05 vs. baseline, respectively), whereas no significant changes were observed during lipid/heparin infusion (P = not significant vs. baseline, respectively). Correspondingly, DHEA and androstendione values were significantly elevated during lipid compared with saline infusion (P < 0.05, respectively), and areas under curve of both androgen precursors were significantly increased with lipid compared with saline infusion. Notably, all changes were detected before induction of insulin resistance.

Conclusions: This study demonstrates that FFAs increase production of androgen precursors in vivo in men. These data tentatively suggest that hyperandrogenemia in polycystic ovary syndrome may be induced, at least in part, by elevated FFAs.


   Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
BASED ON A considerable amount of data in women with polycystic ovary syndrome (PCOS), insulin resistance has been suggested to be a major driver of hyperandrogenemia. Thus, androgen levels were positively correlated with hyperinsulinemia (1). In addition, basal and ACTH-stimulated adrenal androgens were elevated in patients with PCOS and type 2 diabetes mellitus compared with PCOS women with normal glucose tolerance and controls (2). Treatment with insulin-sensitizing agents improved androgenic features in obese and nonobese PCOS patients (3, 4, 5, 6). A potential mechanism was suggested by in vitro studies demonstrating that insulin increases the adrenal sulfotransferase activity, thereby stimulating secretion of the androgen precursor dehydroepiandrosterone sulfate (DHEAS) (7).

However, elevated free fatty acids (FFAs) have also been associated with insulin resistance and have been described to induce peripheral and hepatic insulin resistance (8, 9, 10), raising the question of whether primarily insulin resistance or FFAs induce hyperandrogenemia.

Interestingly, a cumulating set of data suggests a regulation of androgens by dietary fat (11, 12, 13). Black South African men with a customary low-fat diet had lower levels of urinary androgens than North American Black or white men on high-fat diets (14). An elevation of testosterone levels was described during a high-fat, low-fiber diet in healthy men (15). Vice versa, a decrease of DHEAS, androstenedione, testosterone, and 5{alpha}-dihydrotestosterone was demonstrated during a low-fat, high-fiber diet (12). In contrast to long-term effects of a diet, a single complex meal results in an acute postprandial reduction of FFA levels. Interestingly, this was associated with reduced testosterone levels, whereas LH secretion was not modified. Again these data suggest that changes in fatty acids may also modulate androgen production (11).

Making things more complex, regulation of androgen production may be tissue specific, and FFAs might have different effects on adrenal or ovary androgen production. It is well accepted that both ovary and adrenal androgens contribute to hyperandrogenemia in PCOS (16). Although the adrenal cortex is the primary source of androgen precursors in women, dehydroepiandrosterone (DHEA), DHEAS, and androstenedione are also produced in relevant amounts in the ovaries (17, 18). In contrast, in men, at least the androgen precursors DHEA, DHEAS, and androstenedione are nearly exclusively (if not completely) produced in the adrenal gland (19, 20). To exclude potentially opposed effects of FFAs in ovary and adrenal gland and to exclusively investigate the effects of FFAs on the adrenal production of androgen precursors, we decided to investigate healthy men within this study.

In summary, there is considerable evidence that FFAs might modulate androgen production. Despite these tempting data, the role of FFAs on the regulation of androgens has not been investigated in vivo yet. Therefore, we evaluated in a randomized controlled crossover trial, whether FFAs directly affect adrenal production of androgen precursors in vivo.


   Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Subjects

Eight healthy male volunteers were investigated in this randomized controlled crossover trial. The anthropometric and metabolic characteristics of participants are shown in Table 1Go. All participants were initially screened for any systemic disease or biochemical evidence of impaired hepatic or renal function. Diabetes, impaired glucose tolerance, or impaired fasting glucose were excluded by oral glucose tolerance test (21). None of the participants was taking any medication during the study. Body weights were stable for at least 2 months before the study. Informed written consent was obtained from each participant. The study protocol was approved by the Institutional Review Board of the Charité Medical School, Campus Benjamin Franklin.


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  		TABLE 1. Baseline characteristics of study subjects

 
Study design

Each subject was studied with a 2-d protocol in random order. To avoid interactions between the study procedures, the study was performed at intervals of at least 2 d. After a 10-h overnight fast at 0800 h, a short polyethylene catheter was inserted into an antecubital vein for infusion of test substances. Another catheter was placed into the contralateral forearm vein for blood sampling.

Euglycemic hyperinsulinemic clamp with lipid or saline infusion

On day A, 0.9% saline infusion plus heparin (0.4 U/kg·min) was infused at a rate of 1.5 ml/min. Four hours after the start of the saline/heparin infusion, a euglycemic hyperinsulinemic clamp (22) was started in six subjects. The euglycemic hyperinsulinemic clamp started at 2400 h and continued at least 2.5 h using 40 mIU/m2·min human insulin (Actrapid; Novo Nordisk, Bagsvaard, Denmark) and a variable infusion of 10% glucose (Serag Wiessner, Naila, Germany). The priming dose of insulin was calculated as described (22). Capillary glucose concentration was monitored every 5 min and was maintained between 4.0 and 4.9 mmol/liter via variation of the glucose infusion rate.

On day B the same procedure was carried out. But instead of the saline/heparin infusion, Abbolipid 20% (Abbott, Wiesbaden, Germany) plus heparin (0.4 U/kg·min) was infused at a rate of 1.5 ml/min for 6 h.

On both days, blood samples for DHEA, androstenedione, 17-OH-progesterone, testosterone, estrone, LH, FSH, ACTH, cortisol, insulin, and FFAs were collected before and 2 and 4 h after start of the lipid/heparin or saline/heparin infusion, and at least during steady-state conditions of the euglycemic hyperinsulinemic clamp.

Laboratory tests

After sampling in EDTA or serum tubes, blood was immediately chilled on ice and centrifuged at 4 C. Subsequently, aliquots were immediately frozen at –80 C until assayed.

Blood samples were analyzed for ACTH, cortisol, and testosterone by the full automatic chemilumniscence-immunoassay-system IMMULITE from DPC Biermann (Bad Nauheim, Germany) [intraassay coefficient of variation (CV) ranged from 6.7–9.5, 5.2–7.4, and 7.2–16.3%, respectively; interassay CV was 8.5, 7.8, and 12.0%, respectively].

Estrone, 17-OH-progesterone, DHEA, and androstenedione were determined by specific RIAs (Diagnostic Systems Laboratories, Inc., Sinsheim, Germany) (intraassay CV ranged from 4.4–9.4, 8.1–9.5, 2.7–3.8, and 2.7–5.9% respectively; interassay CV was 9.1, 8.9, 6.5, and 6.0%, respectively).

DHEA and androstenedione were also determined after the lipid infusion was added to serum in vitro. A concentration of 2.5% lipid infusion, which results in an increase of triglycerides above the levels reached during lipid infusion, had no effect on DHEA and androstenedione measurement. We thereby ruled out potentially interacting effects of the increased lipid levels on the measurement of DHEA and androstenedione.

LH and FSH were measured by an immunoradiometric assay system (Immuno-Biological Laboratories, Inc., Hamburg, Germany) (intraassay CV 1.6–3.1 and 3.5–6.5% and interassay CV 4.7 and 6.7%, respectively).

Capillary blood glucose was measured during euglycemic hyperinsulinemic clamp every 5 min using the glucose oxidase method on a Dr. Müller Super GL (Freital, Germany). Insulin was measured in plasma by ELISA (DRG, Marburg, Germany). Interassay CV was 12% and intraassay CV was 8%. Nonesterified fatty acids were quantified in serum using a commercially available calorimetric assay (NEFA C; Wako, Neuss, Germany) performed on Cobas Mira (Roche, Basel, Switzerland) (interassay CV was 4.7% and intraassay CV was <5%).

Statistics

Statistical calculations were performed using SPSS version 11.5 (SPSS Inc., Chicago, IL). Data were compared by paired Student’s t test for normally distributed data and Wilcoxon test for skewed data. In addition, profiles of FFAs, cortisol, ACTH, insulin, androstenedione, DHEA, DHEAS, testosterone, estrone, LH, FSH, progesterone, and 17-OH-progesterone were compared by repeated measures ANOVA. Area under curve (AUC) was calculated by using the trapezoid method. Results were considered to be significant if the two-sided {alpha} was less than 0.05. Data are presented as the mean ± SEM unless otherwise mentioned.


   Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
There was no baseline difference of FFAs before lipid/heparin and saline/heparin infusion [0.70 ± 0.23 vs. 0.91 ± 0.27 mmol/liter; P = not significant (n.s.)]. Lipid infusion increased FFAs as expected (P < 0.001 for 2 and 4 h vs. baseline, respectively), whereas there was no increase of FFAs during saline/heparin infusion (n.s. for each time point vs. baseline). However, as expected, a decrease of FFAs was observed during insulin infusion (steady-state) (1.24 ± 0.15 vs. 0.22 ± 0.13 mmol/liter; P < 0.005) (Fig. 1Go).


Figure 1
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  		FIG. 1. FFAs during lipid/heparin infusion ({blacksquare}) vs. saline/heparin infusion ({square}). *, P < 0.005 vs. saline/heparin infusion.

 
Glucose levels were unchanged during both lipid and saline infusion (baseline vs. 4 h: 5.5 ± 0.3 vs. 5.3 ± 0.2 mmol/liter and 4.9 ± 0.2 vs. 4.8 ± 0.1 mmol/liter, respectively; P = n.s.). Comparably, no significant differences were observed between insulin levels during lipid and saline infusion before and 2 and 4 h after start of infusion (Table 2Go). During clamp, insulin levels increased significantly during both lipid and saline infusion (56.5 ± 5.6 vs. 5.81 ± 1.26 mU/liter and 54.2 ± 2.7 vs. 3.37 ± 0.70 mU/liter, respectively; P < 0.001).


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  		TABLE 2. Insulin and HOMA values during saline and lipid infusion

 
Insulin sensitivity during lipid infusion was additionally assessed by homeostasis model of assessment-insulin resistance (HOMA-IR), which was calculated as previously described (23). As expected and previously described (24), no significant changes in insulin sensitivity were observed 2 h after start of lipid infusion, as demonstrated by unchanged HOMA-insulin resistance values (1.23 ± 0.29 vs. 1.17 ± 0.24; P = n.s.). Mean insulin and HOMA values during saline and lipid infusion are presented in Table 2Go.

After 6 h, lipid infusion induced insulin resistance as demonstrated by a reduced M-value (glucose infusion rate per kilogram of body weight) compared with saline infusion (4.08 ± 2.15 vs. 6.02 ± 2.60 mg/kg·min; P < 0.005) (8, 9).

Androstenedione showed a progressive decline during saline/heparin infusion at 2 and 4 h compared with baseline levels (2.09 ± 0.12 vs. 1.53 ± 0.11 ng/ml and vs. 1.49 ± 0.08 ng/ml; P < 0.05). However, no decline in androstenedione levels could be observed at 2 and 4 h of lipid/heparin infusion. Thus, levels of androstenedione were significantly elevated 2 and 4 h after start of lipid/heparin infusion compared with saline/heparin infusion (P < 0.05). AUC of androstenedione was significantly increased during lipid/heparin compared with saline/heparin infusion (479 ± 33 vs. 397 ± 23 ng/ml·min; P < 0.05). During steady-state there were no significant changes of androstenedione (Fig. 2Go), independent of whether lipid or saline/heparin infusion was previously applied.


Figure 2
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  		FIG. 2. Androstenedione during lipid/heparin infusion ({blacksquare}) vs. saline/heparin infusion ({square}). *, P < 0.05 vs. saline/heparin infusion. AUC was 479 ± 33 ng/ml·min during lipid/heparin infusion vs. 397 ± 23 ng/ml·min during saline/heparin infusion (P < 0.05).

 
17-Hydroxyprogesterone levels showed the physiological circadian decline during saline/heparin infusion (P < 0.05), and this decline was also observed during lipid/heparin infusion. Correspondingly, the AUC of 17-hydroxyprogesterone did not differ between lipid and saline infusion (619 ± 85 vs. 526 ± 39 ng/ml·min, respectively; P = n.s.). (Fig. 3AGo).


Figure 3
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  		FIG. 3. 17-Hydroxyprogesterone (A) and DHEA (B) during lipid/heparin infusion ({blacksquare}) vs. saline/heparin infusion ({square}). P < 0.05 for lipid/heparin and saline/heparin infusion. AUCs were 619 ± 85 and 4263 ± 461 ng/ml·min during lipid/heparin infusion vs. 526 ± 39 and 3459 ± 380 ng/ml·min during saline/heparin infusion for 17-hydroxyprogesterone and DHEA, respectively (P = n.s. and P < 0.05, respectively). *, P < 0.05 vs. saline/heparin infusion.

 
DHEA levels declined during saline/heparin infusion at 2 and 4 h (21.3 ± 2.1 vs. 12.3 ± 2.2 vs. 11.5 ± 0.8 ng/ml; P < 0.05), whereas no reduction was observed at 2 and 4 h during lipid/heparin infusion. Compared with saline/heparin infusion, DHEA was significantly increased 2 and 4 h after start of lipid/heparin infusion (P < 0.05). The AUC of DHEA was significantly different between lipid and saline infusion (4263 ± 461 vs. 3459 ± 380 ng/ml·min, respectively; P < 0.05). No significant changes of DHEA levels were observed during steady-state conditions, independent of whether lipid/heparin or saline/heparin infusion were analyzed (Fig. 3BGo).

No differences of DHEAS were found at baseline before start of lipid or saline infusion (3250.5 ± 228.4 vs. 3039.4 ± 223.8 ng/ml; P = n.s.). DHEAS levels did not change during saline infusion, whereas even an increase was observed during lipid infusion at 2 and 4 h (3250.5 ± 228.4 vs. 3683.6 ± 252.3 vs. 3608.9 ± 175.6 ng/ml; P < 0.05). Significantly higher levels of DHEAS were observed during lipid/heparin infusion at 2 and 4 h after start of infusion compared with the corresponding time points of saline infusion (3683.6 ± 252.3 vs. 3021.9 ± 258.9 and 3608.9 ± 175.6 vs. 2892.4 ± 202.5 ng/ml; P < 0.05, respectively). Correspondingly, the AUC of DHEAS was higher during lipid compared with saline infusion (853,597.5 ± 53,388.4 vs. 718,530.0 ± 55,933.0 ng/ml·min; P < 0.05). The DHEA to DHEAS ratio was not different at baseline or at 2 and 4 h after start of infusion (data not shown).

Testosterone levels during lipid/heparin infusion were not different from testosterone levels observed during saline/heparin infusion. Furthermore, there was no difference of the AUC of testosterone during lipid/heparin and saline/heparin infusion (12,468 ± 1,243 vs. 12,384 ± 1,951 nmol/liter·min; P = n.s.) (Fig. 4AGo).


Figure 4
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  		FIG. 4. Testosterone (A) and estrone (B) during lipid/heparin infusion ({blacksquare}) vs. saline/heparin infusion ({square}). AUCs were 12,468 ± 1,243 nmol/liter·min and 30,863 ± 2,647 pg/ml·min during lipid/heparin infusion vs. 12,384 ± 1,951 nmol/liter·min and 17,238 ± 1,970 pg/ml·min during saline/heparin infusion for testosterone and estrone, respectively (P = n.s. and P < 0.05, respectively). *, P < 0.05 vs. saline/heparin infusion.

 
No changes of estrone were observed at 2 and 4 h during saline/heparin infusion. However, estrone showed a progressive increase during lipid/heparin infusion at 2 h, at 4 h, and during hyperinsulinemia compared with baseline levels (60.6 ± 8.1 vs. 133.9 ± 12.7 pg/ml and vs. 186.7 ± 30.1 and vs. 132.5 ± 19.9 pg/ml; P < 0.05). Thus, estrone levels during lipid/heparin infusion were elevated at all time points compared with saline/heparin infusion (P < 0.05). In accordance with these findings, the AUC was increased during lipid infusion (30,863 ± 2,647 vs. 17,238 ± 1,970 pg/ml·min; P < 0.05) (Fig. 4BGo).

ACTH levels did not differ before start of either lipid or saline infusion. During saline/heparin infusion, plasma ACTH decreased, which was comparable to the decline observed during lipid/heparin infusion. ACTH levels at 2 and 4 h after start of infusion were not different from ACTH during steady-state of euglycemic hyperinsulinemic clamp, both during saline infusion and lipid infusion. Correspondingly, we found no differences in serum cortisol during saline infusion and lipid infusion at any time point.

There were no differences in LH and FSH during lipid infusion compared with saline infusion (AUCs: LH 945 ± 89 vs. 1045 ± 109 U/liter·min, respectively, and FSH 935 ± 98 vs. 971 ± 153 U/liter·min, respectively; P = n.s.) (Fig. 5Go, A and B).


Figure 5
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  		FIG. 5. FSH (A) and LH (B) during lipid/heparin infusion ({blacksquare}) vs. saline/heparin infusion ({square}). AUCs were 945 ± 89 and 935 ± 98 U/liter·min during lipid/heparin infusion vs. 1045 ± 109 and 971 ± 153 U/liter·min during saline/heparin infusion for LH and FSH, respectively (P = n.s. for both).

 

   Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
This controlled, randomized crossover trial demonstrates that FFAs elevate the androgen precursors DHEA and androstenedione in vivo. Because effects on androgen precursors were observed as early as 2 h after raising FFAs, this effect appears to be independent of subsequent changes in insulin sensitivity.

In our study, FFAs induced an increase of androstenedione, which is synthesized from 17-OH-progesterone or from DHEA. 17-OH-progesterone levels were not differently influenced by lipid or saline infusion, suggesting that androstenedione production was not increased via this pathway. In contrast, we observed increased DHEA levels during lipid infusion, which suggests that elevation of androstenedione is induced by increased production of its precursor DHEA. As both androgen precursors were elevated within 2 h, it is unlikely that FFAs induce effects on the mRNA expression of rate limiting enzymes, but suggest direct effects on enzyme activities and substrate fluxes. DHEA and DHEAS are steroids predominantly secreted from the adrenal cortex in men (19, 20, 25, 26, 27, 28, 29). Therefore, we assume that the effects of elevated FFAs are basically due to increased adrenal androgen production. Interestingly, we did not find a lipid-induced difference of 17-hydroxyprogesterone levels. An increased 17{alpha}-hydroxylase activity of P450c17 would result in elevated levels of 17-hydroxypregnenolon, DHEA, and 17-hydroxyprogesterone. However, a relatively increased lyase activity of the enzyme would result in an increase of DHEA, but not of 17-hydroxyprogesterone, as found in our study. Most interestingly, a differential regulation of the activity of this enzyme has been found in patients with poorly controlled type 2 diabetes mellitus, which are known to have elevated FFAs (30). Comparably, an acute elevation of insulin into the high physiological range has been demonstrated to selectively inhibit adrenal 17,20-lyase activity (31). It is tempting to speculate that this effect might be a result of reduced FFAs during hyperinulinemia.

Another potential mechanism resulting in increased DHEA levels might be a modulation of FFAs on hepatic sulfotransferase activity with increased levels of DHEA and decreased DHEAS levels. However, no reduction of DHEAS was observed during lipid infusion. Correspondingly, the DHEA to DHEAS ratio did not change during lipid infusion, making differences in hepatic sulfotransferase activity rather unlikely. If sulfotransferase activity changed at all, our data would imply an activation of this enzyme, making differences in DHEA production even more pronounced.

We investigated healthy male subjects, because we aimed to exclude potential opposite effects of ovary and adrenal androgen production during treatment with FFAs. It is unclear whether ovary production of androgens in women is comparably regulated, but it is tempting to speculate that the hyperandrogenemia in women with PCOS, at least in part, may depend also on elevated FFAs. To dissect the adrenal and extraadrenal regulation of androgens in more detail, future studies addressing this question, such as studies after pretreatment with a long-acting GnRH analog would be desirable.

Androstenedione is the precursor of both testosterone and estrone. Indeed we found increased levels of estrone, whereas testosterone levels were unchanged. Interestingly, studies on the pharmacokinetics and bioconversion of DHEA in humans revealed that DHEA administration leads to a sexually dimorphic conversion pattern with significant increases in circulating androgens in women (32), but increased circulating estrogens in men (33). These data suggest that DHEA may have gender-specific effects and induce androgenic effects in women and estrogenic effects in men. Thus, it is reasonable to speculate that the effects on DHEA and androstenedione by FFAs described in this study might result in hyperandrogenemia in women, whereas, in healthy young men, the physiological response with an increase of estrone can be observed during lipid infusion.

Elevation of circulating FFAs is well known to induce insulin resistance and hyperinsulinemia (8, 9, 34). Indeed, an association of insulin resistance, hyperinsulinemia, and hyperandrogenism has been demonstrated in women with PCOS (1). In this study, which aimed to investigate the effects of FFAs on the production of androgen precursors, short-term hyperinsulinemia during steady-state had no effect on any of the investigated androgens. However, corresponding to the elevation of insulin we observed a reduction of FFAs. Thus, any direct effect of insulin might have been counterbalanced by the reduction of FFAs, which is likely given the above mentioned data after isolated elevation of FFAs. In comparison, postprandial suppression of FFAs might explain decreased androgens after oral glucose load, such as shown in women with PCOS and healthy controls (35, 36). However, our study was a short-term intervention, and whether such mechanisms are relevant on the long term, needs to be demonstrated in future studies.

Although an elevation of FFAs is able to induce insulin resistance, this effect is well known to occur not earlier than about 210 min after lipid infusion (24), whereas the effect on androgen precursors was found after 2 h. At that time point, insulin resistance was approximated by measurement of HOMA-IR, which was unchanged compared with baseline values suggesting that insulin sensitivity was not changed as early as 2 h after the beginning of lipid infusion. Thus, the effect of FFAs appears to be independent of a subsequently induced insulin resistance in this study. However, this interpretation is based on previous findings on the time course of lipid-induced insulin resistance and the measurement of HOMA, which is not established to determine insulin sensitivity during fat infusion. Although we believe that using HOMA is a possible approach in this setting and a considerable amount of data suggests that insulin sensitivity is not affected earlier than 3 h, it may be a critical point and future studies addressing the question are desirable.

Adrenal production of androgens is known to be partially under central control (25). However, ACTH and gonadotropin levels were not affected by FFAs. Thus, the effects are likely to result from direct actions on the adrenal cortex. In accordance with these findings, no central inhibitory effect was suggested to account for the decreased androgens by diet modulation (12). The precise molecular mechanism of our observations remains unclear and should be elucidated in future studies. Especially the relationship between preexisting anthropometric and metabolic phenotype with the androgen response may be of special interest. Although no differences between DHEA and androstenedione response to lipid infusion were found with respect to anthropometric markers such as body mass index, this study was not designed, and therefore clearly underpowered, to investigate effects of body weight on FFA-induced changes of androgens.

In summary, this is the first study presenting reasonable evidence that elevation of FFAs increases production of androgen precursors in vivo. The modulation of androgen secretion was presumably independent of subsequently induced changes of insulin resistance. We tentatively speculate that comparable mechanisms might be relevant in the development of hyperandrogenemia in women with PCOS.


   Acknowledgments
 
We thank P. Exner, K. Sprengel, and B. Bredigkeit for excellent technical assistance; B. Wegner for help in measurement of specific androgens; and K. Hoffmann for statistical advice.


   Footnotes
 
This study was supported by Eli-Lilly International Foundation and the German Diabetes Association. J.S. and A.F.H.P. are supported by the Bundesministerium für Bildung und Forschung.

The authors have no conflicts of interest to declare.

First Published Online January 24, 2006

Abbreviations: AUC, Area under curve; CV, coefficient of variation; DHEA, dehydroepiandrosterone; DHEAS, DHEA sulfate; FFA, free fatty acid; HOMA, homeostasis model of assessment; HOMA-IR, HOMA-insulin resistance; n.s., not significant; PCOS, polycystic ovary syndrome.

Received September 16, 2005.

Accepted January 13, 2006.


   References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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Letter re: Free Fatty Acids and Androgen Precursors in Vivo
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