Hypoglycemia-induced suppression of luteinizing hormone (LH) secretion in intact female rhesus macaques: role of vasopressin and endogenous opioids.
The first objective of this study was to determine whether insulin-induced hypoglycemia (IIH) inhibits LH secretion in unrestrained female macaques during the follicular phase of the menstrual cycle. There was a consistent inhibitory effect of hypoglycemia on LH secretion within 3 h in these females. This inhibition was likely an indirect effect since low glucose levels did not inhibit GnRH secretion from GT1-1 neurones in vitro. We next investigated whether administration of a vasopressin antagonist (AVPa) either alone, or with naloxone could reverse the IIH-induced inhibition of LH release. Females were studied in the follicular phase during 10 h periods with blood samples collected every 10 min. Experimental groups were IIH (n=6), IIH+AVPa (n=5) and IIH+AVPa+naloxone (n=4). The first 5 h of each study served as a control and hypoglycemia was then induced with insulin. The AVPa was given as a bolus (180 microg) just before the insulin and was followed by a continuous infusion (180 microg/h) for 5 h. Naloxone (5 mg/kg) was given with the AVPa and followed by a continuous infusion (5 mg/kg/h) for 5 h. In the IIH group, LH reached its lowest value 3-4 h after insulin. Neither AVPa nor AVPa+naloxone infusion reversed the inhibitory action of hypoglycemia on LH release. These data suggest that if there are inhibitory actions of vasopressin and endogenous opioids on GnRH release induced by hypoglycemia, they are not sufficient to explain the suppression of GnRH/LH release in intact female primates.
Lado-Abeal
Joaquin
J
Cell Biology and Biochemistry, 3601 4th Street, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.
Clapper
Jeffrey A
JA
Chen Zhu
B
B
Hough
Corey M
CM
Syapin
Peter J
PJ
Norman
Reid L
RL
D000818:Animals; D001127:Arginine Vasopressin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D001786:Blood Glucose / Q000378:metabolism; D003346:Corticotropin-Releasing Hormone / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004723:Endorphins / Q000502:physiology*; D005260:Female; D006854:Hydrocortisone / Q000097:blood; D007003:Hypoglycemia / Q000097:blood / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D008253:Macaca mulatta; D008597:Menstrual Cycle / Q000502:physiology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D014667:Vasopressins / Q000502:physiology*
D001786:Blood Glucose; D004723:Endorphins; D007004:Hypoglycemic Agents; D007328:Insulin; D009292:Narcotic Antagonists; D014667:Vasopressins; D001127:Arginine Vasopressin; D009270:Naloxone; D007986:Luteinizing Hormone; D003346:Corticotropin-Releasing Hormone; D006854:Hydrocortisone