RESTRAINT INHIBITS LUTEINIZING-HORMONE SECRETION IN THE FOLLICULAR PHASE OF THE MENSTRUAL-CYCLE IN RHESUS MACAQUES

The present study investigated the question of how restraint affects t he the hypothalamo-pituitary adrenocortical axis and the the hypothala mo-pituitary gonadal axis in intact, adult female rhesus macaques in b oth the follicular and luteal phases of the menstrual cycle. Restraint was chosen because it is not physically harmful to the animal but rat her serves primarily as a psychological stressor. Blood samples were c ollected from a remote site at 15-min intervals beginning at 0700 h fr om tethered adult female rhesus macaques. Each animal was subjected to 6 h of chair restraint after a 3-h control period in the animal's hom e cage. Samples were collected for an additional 6 h after the end of the restraint period, when each animal was returned to Its home cage. Brief anesthesia with ketamine (administered through indwelling cathet er) facilitated transfer of the animals to and from the chair Blood sa mples were also collected from undisturbed females in both the follicu lar and luteal phases to document LH, cortisol, and progesterone secre tion throughout the day. Plasma ACTH and cortisol, measured as indices of stress, were elevated within 15 min after initiation of restraint and remained elevated after the animals were returned to their cages. In animals sampled in the follicular phase, mean plasma LH levels were lower during restraint and remained suppressed for several hours afte r the animals were removed from restraint. LH levels were not signific antly inhibited by restraint in the luteal phase. When the opiate rece ptor antagonist naloxone (Nx; 5 mg bolus plus 5 mg/h) was given beginn ing 2 h after the initiation of restraint, LH levels were elevated com pared to prerestraint levels in both phases of the menstrual cycle. Th ese data indicate that restraint is a potent activator of the pituitar y-adrenal axis and that at least in the follicular phase of the menstr ual cycle, restraint inhibits pituitary LH release. This inhibition of gonadotropin release may involve endogenous opiate suppression of GnR H release, since Nx reversed the effect of restraint