Jl. Cameron et al., MODULATION OF REPRODUCTIVE HORMONE-SECRETION BY NUTRITIONAL INTAKE - STRESS SIGNALS VERSUS METABOLIC SIGNALS, Human reproduction, 8, 1993, pp. 162-167
States of chronic undernutrition can cause a profound suppression of r
eproductive function. To begin to determine the time course and the na
ture of the mechanism by which undernutrition suppresses the activity
of the reproductive axis we have examined the effects of brief periods
of fasting on reproductive hormone secretion in men and male rhesus m
onkeys. In monkeys there is a significant suppression of pulsatile lut
einizing hormone (LH) and testosterone secretion after a single day of
fasting, that is apparent within the first 4 h after a meal is missed
. The suppression of pulsatile LH secretion on a day of fasting does n
ot appear to be caused by the psychological stress experienced when mo
nkeys are deprived of their daily meal in that monkeys who are maintai
ned in a metabolically fed state (by feeding a large excess of food on
the day prior to fasting), but are deprived of a meal and displayed b
ehavioural agitation associated with fasting, have no suppression of L
H secretion. The suppression of LH secretion on a day of fasting canno
t be reversed by naloxone infusion, indicating that increased secretio
n of opioid peptides is not the primary mechanism causing the decrease
in the central drive to the reproductive axis during fasting. In addi
tion, although there is a mild activation of the adrenal axis, with sl
ight rises in plasma adrenocorticotropic hormone (ACTH) and cortisol c
oncentrations on a day of fasting, the increased activity of the adren
al axis does not appear to cause the fasting-induced suppression of LH
secretion, since there is no correlation between the magnitude of the
rise in cortisol secretion and the degree of suppression of LH secret
ion during fasting, and dexamethasone injections, which inhibit the ce
ntral drive to the adrenal axis, fail to prevent fasting-induced suppr
ession of LH secretion. Cumulatively these findings argue against the
hypothesis that a general stress response to fasting causes the fastin
g-induced suppression of reproductive axis activity. Alternatively, it
seems more likely that signals specifically occurring as a result of
changes in the metabolic state of the body may be causing the suppress
ion of reproductive hormone secretion that occurs during the early sta
ges of fasting.