Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science


Hypothalamic control of luteinizing hormone (LH) secretion was investigated in crossbred beef heifers by comparing anterior (AHD), posterior (PHD), and complete (CHD) hypothalamic deafferentation with sham operated controls (SOC). Heifers (n = 16) were fitted with an indwelling jugular catheter 6 days before cranial surgery, and assigned randomly to treatments. Blood for RIA of LH was collected sequentially at 15-min intervals during an 8-h period on days -5, -1 before and day 6 after hypothalamic deafferentation or sham operation. On the day of surgery, blood samples were collected sequentially at 15-min intervals 2 h before induction of anesthesia and throughout surgery and early recovery. Seven months after hypothalamic deafferentation all experimental and sham operated heifers were ovariectomized and treated with vegetable oil (i.m.) plus saline (i.v.), vegetable oil plus LH-releasing hormone (LHRH), estradiol benzoate (EB, 1 mg) in vegetable oil (i.m.) plus saline and EB plus LHRH. Blood samples were collected sequentially for a 30-h period. The amplitude of the LH spikes was reduced (P 0.05) in amplitude or frequency of LH spikes were observed in PHD or SOC groups. Injection of 50 (mu)g LHRH 7 days after hypothalamic deafferentation of sham operation resulted in an abrupt increase (P 0.05) in the overall mean LH plasma concentrations during 30-h bleeding period. Injection of vegetable oil plus saline elicited a significant increase (P < 0.001) in LH peripheral concentrations. The amplitude of LH spikes in response to LHRH was greater (P < 0.01) in CHD and PHD when compared with SOC and AHD heifers. Injection of EB failed to induce a preovulatory-like LH surge in CHD and PHD when compared with SOC and AHD heifers. Injection of EB plus LHRH elicited LH release in all experimental and sham operated heifers.



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Jose Ramon Molina-Villalobos



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231 pages