This Article Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via Google Scholar Google Scholar Articles by CAREY, R. M. Articles by SEIF, S. M. Search for Related Content PubMed PubMed Citation Articles by CAREY, R. M. Articles by SEIF, S. M.

The Effects of Ovine Prolactin on Water and Electrolyte Excretion in Man Are Attributable to Vasopressin Contamination

Divisions of Endocrinology, Departments of Internal Medicine and Pediatrics, University of Virginia School of Medicine, Charlottesville, Virginia, and the Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania

Reprint requests to: Dr. Robert M. Carey, Box 146, University of Virginia Hospital, Charlottesville, Virginia 22901.

Prolactin is an important osmoregulatory hormone in several lower vertebrate species. The present study was undertaken to clarify the effects of prolactin, if any, on human renal function. Eight normal adult male subjects on a 150 mEq sodium (Na), 60 mEq potassium (K) diet for 5 days were studied during 12 h of oral water (H₂O) loading on 2 consecutive days. On day 1, after a 6 h control period, a 1 ml normal saline placebo was given im; on day 2, 25 mg of ovine prolactin (OP) was substituted. The subjects were supine and received a constant infusion of Na and K. After OP, serum prolactin rose from 6.9 ± 0.8 ng/ml to 15.0 ± 2.5 ng/ml (P < .01) at 1 h, 27.6 ± 4.0 ng/ml (P <.002) at 2 h, 33.1 ±4.3 ng/ml (P <.001) at 3 h and remained elevated for the remaining 3 h of study. The ovine prolactin had 20– 25% of the potency of human prolactin in the human prolactin radioimmunoassay system. In response to OP, free H₂O clearance (C_H2o) promptly decreased from 10.1 ± .06 ml/min to 6.1 ± .05 ml/min (P <.01) at 1 h, to a nadir of 5.1 ±.3 ml/min (P <.001) at 2 h, and returned to control levels by 4 h. C_H2o was unchanged after placebo, and urinary Na and K excretion, creatinine and osmolar clearance (C_osm), plasma Na, K, osmolality and aldosterone were unchanged after OP or placebo. Control plasma vasopressin was 1.0 ± 0.1 µ U/J/ml and was not changed after prolactin (1.1 ± 0.1 µ U/ml at 1 h, 1.1 ± 0.1 < µU/ml at 2 h and 1.1 ± 0.1 µU/ml at 3 h). The ovine prolactin contained 2 µU of immunoassayable vasopressin per/ng of powder. Aqueous vasopressin, 50 mU (contained in 25 mg of ovine prolactin), produced a decrease in C_H2o not significantly different from prolactin in 6 water loaded subjects. Four different subjects given 100 mg of OP had decreased C_H2o from 8.3 ±0.3 to 2.7 ± 0.7 ml/min at 1 h (P <.001) and to 2.8 ±0.7 ml/min at 2 h (P <.01). Control plasma osmolality was 301 ± 4 mOsm/1 and decreased to a maximum of 288 ± 5 mOsm/1 4 h after OP (P <.001). After prolactin administration, plasma vasopressin rose from 0.44 ± 0.15 to 0.80 ± 0.41 µU/ml (P = NS) at 1 h. The transient antidiuresis in response to ovine prolactin is due to contamination of the preparation with vasopressin. Prolactin does not acutely influence renal electrolyte excretion and probably does not influence water excretion in man.

Supported by USPHS General Clinical Research Center Grant RR-847 and in part by USPHS Grants AM-17523 and AM-16166. Dr. Carey is an Established Investigator of the American Heart Association.

Presented at the 58th Annual Meeting of the Endocrine Society, San Francisco, California, June 1976.

Received July 1, 1976.