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Stimulation of rhesus monkey GH release: arginine vs plasma volume expansion
Abstract:
Plasma GH and cortisol responses were examined in unanesthetized adult male rhesus monkeys infused with approximately 30 ml (8.3 ml/kg) of arginine monohydrochloride (Arg 0.5 g/kg), 0.9% saline (NS) or Dextran 75 and following 15 ml infusions of acid-saline (AS), or somatostatin (GHRIH 30 mug/kg). None of the infusions were accompanied by GH elevations. Rebound GH elevations occurred after each 30 ml infusion and after GHRIH but not after 15 ml AS. Although the amplitude of GH responses were not significantly different (p greater than 0.05), responses to Arg and dextran were significantly delayed as compared to responses following NS and GHRIH which did not differ from each other. Both of the latter responses occurred within 15 min of infusion completion. The delay following dextran was significantly longer than that following Arg (p less than 0.05). Since the volume of saline and the dosage of Arg were equivalent to those used in the standard intravenous Arg test, results suggest that effects of infusion volume upon GH secretion and upon GH responses to Arg warrant examination in the human. In addition, it is suggested that GH responses to NS and to dextran are mediated via an intravascular volume control mechanism and that GHRIH may be released upon activation of such a mechanism. GH elevations may represent rebound responses upon termination of GHRIH secretion.
Insights
Rebound growth hormone (GH) elevations occurred after 30 ml infusions of arginine or dextran, but not after smaller 15 ml infusions. These findings suggest volume-mediated mechanisms influence GH secretion in rhesus monkeys.
Area of Science:
- Endocrinology
- Physiology
Background:
- Growth hormone (GH) secretion is regulated by complex mechanisms.
- Arginine infusion is a standard test for GH response.
Purpose of the Study:
- To investigate plasma GH and cortisol responses in rhesus monkeys following various infusions.
- To explore the role of infusion volume and specific substances on GH secretion.
Main Methods:
- Unanesthetized adult male rhesus monkeys received infusions of arginine monohydrochloride, saline, dextran, acid-saline, or somatostatin (GHRIH).
- Plasma GH and cortisol levels were monitored post-infusion.
Main Results:
- No immediate GH elevations were observed with any infusion.
- Rebound GH elevations occurred after 30 ml infusions (arginine, dextran, saline) and GHRIH, but not 15 ml acid-saline.
- GH responses to saline and GHRIH were rapid (within 15 min), while arginine and dextran responses were significantly delayed.
Conclusions:
- Infusion volume appears to influence GH secretion, suggesting a need for human studies on volume effects.
- GH responses to saline and dextran may involve intravascular volume control mechanisms.
- GHRIH release might be triggered by volume-activated mechanisms, with GH elevations representing rebound secretion.