Influence of season and estradiol on secretion of luteinizing hormone in ovariectomized cows
The hypotheses that secretion of luteinizing hormone (LH) varies with season and that estradiol may modulate the seasonal fluctuation in secretion of LH in cows were investigated. Seven mature cows were ovariectomized approximately 30 days before initiation of the experiment. Three of the ovariectom...
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Veröffentlicht in: | Biology of reproduction 1986-10, Vol.35 (3), p.549-553 |
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Zusammenfassung: | The hypotheses that secretion of luteinizing hormone (LH) varies with season and that estradiol may modulate the seasonal
fluctuation in secretion of LH in cows were investigated. Seven mature cows were ovariectomized approximately 30 days before
initiation of the experiment. Three of the ovariectomized cows (OVX-E2) were administered a subcutaneous estradiol implant
that provided low circulating levels of 17 beta-estradiol. The remaining 4 cows (OVX) were not implanted. From December 21,
1982, to September 20, 1984, blood samples were collected sequentially (at 10-min intervals for 6 h) at each summer and winter
solstice, and each spring and autumn equinox. In addition, from March 17, 1983, to March 17, 1984, sequential samples were
collected midway between each solstice and equinox. Concentration of LH was measured in all samples, and concentration of
estradiol was measured in pools of samples. An annual cycle in mean serum concentration of LH and amplitude of LH pulses was
detected in both groups of cows. The seasonal pattern did not differ in the two treatment groups. Serum concentration of LH
and amplitude of LH pulses were highest around the spring equinox, decreased gradually to the autumn equinox, and then increased
and peaked again during the following spring equinox. Frequency of LH pulses and concentration of estradiol in serum did not
vary with season. Circulating concentrations of LH and amplitude of pulses tended to be higher in OVX-E2 than OVX cows throughout
the experimental period. Frequency of pulses of LH was lower in OVX-E2 than OVX cows throughout the experiment. Concentrations
of estradiol were higher in the implanted cows. |
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ISSN: | 0006-3363 1529-7268 |
DOI: | 10.1095/biolreprod35.3.549 |