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Plasma Growth Hormone Responses to Somatostatin (SRIH) and SRIH Receptors in Pituitary Adenomas in Acromegalic Patients^*

Third Department of Internal Medicine and the Department of Neurosurgery Kyushu University Fukuoka 812,Japan
Faculty of Medicine, Kyushu University Fukuoka 812,Japan

Address requests for reprints to: Dr. Shoichiro Ikuyama, Third Department of Internal Medicine, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812, Japan.

The plasma GH response to somatostatin (SRIH) infusion and SRIH receptors in pituitary adenoma cell membranes were investigated in six acromegalic patients. Infusion of 0.3 and 1.0 µg/kg·h SRIH increased plasma SRIH concentrations in these patients in a dose-related manner. In five of the six patients, mean plasma GH levels decreased to 65.5 ± 5.0% (±SEM) and 43.7 ± 3.1% of the basal level when 0.3 or 1.0 µg/kg·h SRIH was infused, respectively. In the remaining patient, plasma GH levels did not change, even when a larger dose of SRIH was infused. High density and specific SRIH receptors, with a mean dissociation constant of 0.92 ± 0.17 nM and a mean maximal binding capacity of 523.8 ± 174.6 fmol/mg protein, were identified in GH-secreting adenomas from the five SRIH-responsive patients. On the other hand, in the adenoma from the SRIH-nonresponsive patient, the maximal binding capacity (40.5 fmol/mg protein) was as low as those of nonfunctioning adenomas, as reported previously (undetectable to 48.0 fmol/mg protein). We conclude that the differential responses of plasma GH to SRIH in acromegalic patients may be related to variations in the binding capacity for SRIH in adenoma cell membranes.

^* This work was supported in part by a research grant from the Division of Intractable Diseases, the Ministry of Health and Welfare, Japan.

Received August 15, 1985.

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