title: Plasma growth hormone responses to somatostatin (SRIH) and SRIH receptors in pituitary adenomas in acromegalic patients.
abstract: 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 microgram/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 microgram/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.
authors.forename: S
authors.initials: S
authors.lastname: Ikuyama
authors.forename: H
authors.initials: H
authors.lastname: Nawata
authors.forename: K
authors.initials: K
authors.lastname: Kato
authors.forename: H
authors.initials: H
authors.lastname: Ibayashi
authors.forename: H
authors.initials: H
authors.lastname: Nakagaki
mesh_terms: D000172:Acromegaly / Q000097:blood* / Q000209:etiology / Q000378:metabolism; D000236:Adenoma / Q000097:blood* / Q000150:complications / Q000378:metabolism; D000328:Adult; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010911:Pituitary Neoplasms / Q000097:blood* / Q000150:complications / Q000378:metabolism; D011388:Prolactin / Q000097:blood; D011956:Receptors, Cell Surface / Q000378:metabolism; D017481:Receptors, Somatostatin; D013004:Somatostatin / Q000097:blood
chemical_list: D011956:Receptors, Cell Surface; D017481:Receptors, Somatostatin; D013004:Somatostatin; D011388:Prolactin; D013006:Growth Hormone