R. Friedman et al., RESPONSES OF THE BOVINE INFUNDIBULUM TO NORADRENALINE DURING THE ESTROUS-CYCLE, Journal of Reproduction and Fertility, 101(2), 1994, pp. 311-315
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.