Graduate Thesis Or Dissertation
 

The response of the bovine infundibulum to norepinephrine and acetylcholine during estrogen and progesterone dominance

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  • A local effect of endogenous ovarian hormones on the in vitro responses of the bovine infundibulum to the neurotransmitters norepinephrine (NE) and acetylcholine (Ach) was investigated. Prostaglandin F₂α-tham salt was utilized to induce luteal regression in six heifers which were necropsied during proestrus. Six heifers were also necropsied during the mid-luteal phase (day 12) of the estrous cycle. A strip of each infundibulum from each heifer was placed in a tissue bath and exposed to NE (0.4, 0.8, 1.6 μg/ml) followed by Ach (0.1, 0.56, 1.0 μg/ml). Changes in frequency and amplitude of contractions and tissue tone were recorded. Infundibula ipsilateral to the ovary bearing the largest follicle in proestrous heifers responded to all concentrations of NE with greater frequency of contractions than contralateral infundibula or both ipsilateral and contralateral infundibula of diestrous animals (stage of cycle x tissue location interaction, P < .01). Ipsilateral infundibula of proestrous heifers appeared to respond to increasing concentrations of NE with a linear increase in frequency of contractions but the dose-response relationship was statistically nonsignificant. Amplitude of contractions induced by all concentrations of NE studied did not differ between stages of the cycle or between ipsilateral or contralateral infundibula. Mean tone of ipsilateral and contralateral infundibula of proestrous and diestrous animals increased linearly in response to all concentrations of NE (P < .05). Norepinephrine-induced increases in the mean tone of infundibula from diestrous animals were greater than for infundibula of proestrous heifers (P ≈ .06). Frequency of contractions in response to Ach was dependent upon the in vitro neuro transmitter concentration and tissue location within animal (Ach x tissue location interaction, P < .01). Acetylcholine at 0.1 μg/ml inhibited frequency of contractions regardless of stage or location of the infundibulum. In contrast, 0.56 and 1.0 μg/ml Ach increased frequency of contractions of ipsilateral but was without affect or further depressed this response of all contralateral infundibula. Amplitude of contractions in response to Ach was unaffected by cycle stage or infundibula location (P > .05). Ipsilateral and contralateral infundibula at both stages of the cycle exhibited a reduction of mean tone in response to 0.1 μg/ml Ach. In contrast, 0.56 and 1.0 μg/ml Ach caused an increase in the mean tone. These data demonstrate that the bovine infundibulum is responsive to NE and Ach and that these responses are governed by the concentrations of estrogen and progesterone to which the infundibulum is exposed.
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