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North Carolina State University, Raleigh 27695-7621
Abstract
Lactating sows were used to evaluate effects of morphine and suckling on secretion of LH and prolactin (PRL) and occurrence of estrus after weaning. In the first experiment, crossbred multiparous sows nursing 7.9 ± .4 pigs per litter at 25.2 ± .3 d of lactation were subjected to one of three treatments during the middle 8-h segment of a 24-h experimental period. Treatments were infusion (i.v.) of morphine (200 mg/h) with the litter present (n = 4) or transiently weaned (n = 4), or transient weaning of litters without morphine (n = 4). Transient weaning decreased (P < .05) prolactin and increased (P < .05) the frequency of LH pulses and average concentration of LH. Infusion of morphine caused transient hyperthermia and suppressed (P < .05) LH release in two of four sows nursing litters and in four sows whose litters were absent. Infusion of morphine, in the presence or absence of litters, suppressed PRL during the middle and last 8-h segments. A second experiment was conducted to test the hypothesis that chronic administration of morphine delays onset of estrus after weaning. Primiparous Duroc sows were assigned at weaning (53 to 63 d postpartum) to receive morphine (n = 10) or saline (n = 11). Saline (1.5 ml) or morphine (75 mg) was administered s.c. three times a day for 5 d after weaning. Onset of estrus after weaning was delayed in sows given morphine compared with those given saline (9.7 ± .4 vs 5.2 ± .3 d, respectively; P < .05). Days from withdrawal of morphine to estrus (5.7 ± .3) were similar to days from weaning to estrus (5.2 ± .3). These results demonstrate that acute administration of morphine prevented the increase in LH secretion associated with transient weaning and that chronic administration of morphine delayed onset of estrus after weaning, presumably through suppression of LH secretion.
1 Paper No. 10500 of the journal Series of the North Carolina ARS, Raleigh. The use of trade names in this publication does not imply endorsement by the North Carolina ARS of the products named, nor criticism of similar ones not mentioned. Purified porcine LH (LER 786-3) was kindly supplied by L. E. Reichert, Jr. and porcine LH antiserum by G. D. Niswender. Appreciation is expressed to T. Steffel for animal care and to V. Hedgpeth and L. Price-Taras for excellent assistance in performing assays. Supported in part by USDA Grant 85-CRCR-1-1849.
2 Dept. of Anim. Sci., Physiol. Program.
3 Richard B. Russell ARS, USDA, Athens, GA 30613.
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