EVIDENCE SUGGESTING A ROLE OF THE LACTOGENIC HORMONE IN THE ESTROUS CYCLE OF THE ALBINO RAT

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Abstract
Prolactin was successfully employed under certain conditions to induce cyclic ovulation and corpus luteum formation in rats in persistent estrus. In the absence of previously formed lutein tissue it was ineffectual. The evidence indicates that graafian follicles are incapable of secreting progesterone under the stimulus imposed. However, when corpora lutea were first induced by the action of injected progesterone, subsequent adm. of lactogen at certain low dosages resulted in the completion of additional cycles. In several instances, sequences of 2 or more cycles were produced by suitable manipulation of lactogen dose level. Evidence is reviewed which supports an hypothesis that animals of the DA strain are relatively deficient in prolactin output. Defectiveness of the suggested mechanism in DA rats would account for the ease of inducing "light estrus" and, in part, for the early age of onset of spontaneous persistent estrus in that strain.