Increased Lh-Suppressing Effect of Oestrogen in Ovariectomized Rats as a Result of Underfeeding

The ovaries of rats subjected to severe feed restriction undergo atrophy (Piacsek & Meites, 1967; Howland, 1971a, 1972a). The effects of underfeeding on the ovarian function may be related to reduced basal serum LH levels (Howland, 1971b, 1972b). A proposed explanation for the reduced LH secretion in underfed rats is that underfeeding results in increased sensitivity of the hypothalamus to the inhibitory effect of gonadal steroids (Howland, 1971c). This mechanism was suggested by the observation that underfeeding prevented ovarian compensatory hypertrophy (Howland, 1971a, c), a response which is presumably initiated by reduced gonadal steroid levels, but did not prevent the hypersecretion of LH following complete ovariectomy (Howland, 1971c), a condition where there is no ovarian steroid inhibition. The present study was designed to test the hypothesis that the inhibitory effect of oestrogen on LH secretion is increased by underfeeding. Three experiments were conducted using a single pool of ovariectomized rats.