The effect of pituitary-stalk section on light-induced oestrus in ferrets.

Abstract

Beginning on 25 October in the winter of 1951-2, sixteen mature female ferrets, whose pituitary stalks had been completely divided, were kept in artificial light for 6 h at the end of each day. Normal control animals kept under the same conditions came into heat on an average 60 days after the start of the experiment, and about 100 days earlier than when normal ferrets, not exposed to additional light, began their spring oestrus. Ten of the sixteen operated animals reacted to the artificial light, i.e. came into heat, in the same time as did the normal controls. The remaining six were still anoestrous by the time unoperated controls which had not been exposed to additional light had begun their normal spring oestrus. Examination of serial sections showed that animals responded or failed to respond regardless of the re-establishment of a vascular link between the median eminence and the pars distalis of the pituitary. One animal responded in spite of the presence of a plate of paper which formed a complete barrier between the pituitary and the median eminence. In another animal which also responded, the operation had ablated the bed of the primary capillary loops of the pituitary portal vessels and disrupted the floor of the third ventricle.These observations suggest that light-induced oestrus in the ferret is not dependent on the integrity of the pituitary-portal vessels or on any direct hypothalamic innervation of the pars distalis.