MODIFICATION OF THE OESTROUS CYCLE OF THE UNDER-FED RAT INDUCED BY THE PROXIMITY

Dietary restriction in the rat has been shown to affect the oestrous cycle, increasing the length of the di-oestrous period and producing a reduction in the cellular content of the vaginal smear (Mulinos & Pomerantz, 1940). Cooper & Haynes (1967) demonstrated that the introduction of a male to the cage of a female rat subjected to dietary restriction resulted in a shortening of the cycle regardless of the stage at which the male was introduced. In those animals which failed to mate at the first oestrus after introduction of the male (detected by the vaginal smear technique), the subsequent cycle again appeared to be of shorter duration than those before the introduction of the male, indicating that the female continued to respond to the presence of the male. The present work was conducted to examine the induced changes in the oestrous cycle under controlled conditions and in more detail. Eighty nulliparous female rats from a closed colony of Wistar origin were allocated to the experiment. They were 12 weeks old, weighed 120 to 160 g and had completed at least two normal cycles. The rats were caged individuall