Nine male patients 35 to 60 years old received 100 pg synthetic thyrotropin-releasing hormone (TRH) after both an overnight and a 36 hour fast and the serum prolactin response was measured by radioimmunoassay. The prolonged fast significantly (p < 0.05) decreased the mean peak prolactin response from 86.3 ± 25.9 to 32.0 ± 6.2 and the increment above basal from 76.8 ± 24.3 to 27.5 ± 5.5 ng/mJ. There was no change in the pattern or timing of the response and basal values were insignificantly lowered. These observations are discussed in relation to the effects of Casting on glucose, insulin, growth hormone, free fatty acid, ketones and water and electrolyte metabolism.
Arginine is a known stimulus for the secretion of a number of hormones including growth hormone, glucagon, gastrin and insulin. The meehanism of this ubiquitous stimulatory effect is obseure. Aynsley-Green and Alberti (1974) suggested that it may relate to the ability of the guanidine group in arginine to bind to membranes, sinee the N-methylated derivative is inaetivc (Lernmork 1972) and further substitution, c.g. in mctformin and phcnformin actually inhibits insulin release (Schatz, Katsi/Qmbros, Nierle and Pfeiffer 1972)_ Alternatively, arginine could aet by a cholinergic mechanism sinee atropine partially abolishes the insulin response (Aynsley-Green and Albert; 1974) or beeause of the resemblance of the guanidinium ion to triply hydrated $Odium (Paelen; 1960) it may aet by eleetrolyte ehange in the pancreatie beta-cells. Data are represented here which show that the insulin response to arginine is closely related to an inerease in intracellular red blood cell (Rbc) potassium.
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