Enhancing effect of acute fasting on ethanol suppression of pulsatile luteinizing hormone release via an estrogen-dependent mechanism in Holstein heifers

This study was conducted to determine whether acute fasting in Holstein hei fers enhances the suppressive effect of an intravenous injection of ethanol on pulsatile LH release (LH pulse) and, additionally, to establish whether or not the mechanism is estrogen-de-pendent. After estrus synchronization (Day 0 = estrus), 29 heifers were either fasted (fasting group; n = 14) or fully fed as a control (control group; n 15) from Days 1 to 4. On Day 4, bl ood samples were taken at 10-min intervals for 4 h before (pre-injection pe riod) and after (post-injection period) an intravenous injection of 1.5 mi of saline, 1.5 mi of ethanol, or 35 mg of tamoxifen dissolved in 1.5 mL of ethanol. We analyzed the mean LH level, the number of LH peaks per 4 h, and the amplitude of LH peaks. No differences were observed in the LH pulse in the pre-injection period between the control and the fasting group. Howeve r, in the post-injection period, compared with the saline injected control heifers, ethanol suppression of the LH pulse was observed in the number of LH peaks of the ethanol injected control heifers and in all pulse parameter s of the ethanol injected fasting heifers. Furthermore, tamoxifen inhibited suppression of ethanol on LH pulse was observed in the control and fasting heifers injected with tamoxifen dissolved in ethanol. It was concluded tha t acute fasting in Holstein heifers has an enhancing effect on ethanol inhi bition of the LH pulse and that the mechanism may be estrogen-dependent. (C ) 1999 by Elsevier Science Inc.