RESPONSES OF THE BOVINE INFUNDIBULUM TO NORADRENALINE DURING THE ESTROUS-CYCLE

An experiment was conducted to investigate the responses of the bovine infundibulum to noradrenaline in vitro. Twelve beef heifers were kill ed and examined in equal numbers during pro-oestrus and dioestrus (day 12 of the oestrous cycle). A jugular blood sample was collected from each heifer immediately before killing, and the sera were subsequently analysed by radioimmunoassay for progesterone and oestradiol. A strip of each infundibulum (ipsilateral and contralateral to the ovary bear ing the largest follicle or functional corpus luteum) was placed into a tissue bath and sequentially exposed to increasing concentrations of noradrenaline (0.4, 0.8 and 1.6 mu g ml(-1)). Changes in frequency an d amplitude of isometric contractions and tissue tone were recorded. I nfundibula ipsilateral to ovaries bearing the largest follicle in pro- oestrous heifers responded to all concentrations of noradrenaline with greater frequency of contractions than did either contralateral infun dibula or both ipsilateral and contralateral infundibula of dioestrous animals (stage of cycle x tissue location interaction, P < 0.01). Cha nges in the amplitude of contractions induced by noradrenaline did not differ between stages of the cycle studied or the location of the inf undibulum within the animal. Mean tone of ipsilateral and contralatera l infundibula of pro-oestrous and dioestrous animals increased linearl y with exposure to air concentrations of noradrenaline tested (P < 0.0 5). However, the response of infundibula of dioestrous animals was gre ater than that of infundibula of pro-oestrous heifers (P less than or equal to 0.06). These data demonstrate that the bovine infundibulum is responsive to noradrenaline, and suggest that responses to this neuro transmitter may be governed by concentrations of oestrogen and progest erone to which the infundibulum is exposed.