TY - JOUR
T1 - Effect of ovine prolactin administration on hypothalamic vasoactive intestinal peptide (VIP), gonadotropin releasing hormone I and II content, and anterior pituitary VIP receptors in laying Turkey hens
AU - Rozenboim, I.
AU - Tabibzadeh, C.
AU - Silsby, J. L.
AU - El Halawani, M. E.
PY - 1993
Y1 - 1993
N2 - The effect of ovine prolactin (oPRL) administration to laying and incubating turkey hens was studied. In experiment one, five treatment groups (n = 6) of laying hens received injections of vehicle or oPRL (4 mg/bird/day) for 2, 4, 8, or 14 days. Hypothalamic vasoactive intestinal peptide (VIP) content decreased to its lowest level (p < 0.05) by Day 2 of oPRL injection. Serum turkey PRL decreased by Day 8 of injection, reaching nadir by Day 14. Similar to the decline in hypothalamic VIP content, the maximal decline in the number of anterior pituitary VIP binding sites was achieved by Day 2 of oPRL administration. Hypothalamic GnRH-I content decreased after 2 days of oPRL injection and remained low through Day 14 of the experiment. GnRH-II levels declined with time, reaching significantly lower levels after 8 days of injections, and remained low through Day 14. Plasma LH levels also declined (p < 0.05) after Day 14 of oPRL administration. In experiment 2, two groups (n = 6) of incubating birds were used: controls receiving injections of vehicle only and birds receiving injections of oPRL (4 mg/bird/day) for 10 days. Exogenous oPRL had no effect on hypothalamic VIP, GnRH-I or II, anterior pituitary VIP binding sites, or plasma turkey PRL or LH. The findings suggest that in laying hens, PRL inhibits its own secretion by acting on both the hypothalamus and the anterior pituitary; this phenomenon does not occur in incubating birds. Furthermore, we provide evidence that PRL acts centrally to reduce LH levels by reducing GnRH levels in the hypothalamus.
AB - The effect of ovine prolactin (oPRL) administration to laying and incubating turkey hens was studied. In experiment one, five treatment groups (n = 6) of laying hens received injections of vehicle or oPRL (4 mg/bird/day) for 2, 4, 8, or 14 days. Hypothalamic vasoactive intestinal peptide (VIP) content decreased to its lowest level (p < 0.05) by Day 2 of oPRL injection. Serum turkey PRL decreased by Day 8 of injection, reaching nadir by Day 14. Similar to the decline in hypothalamic VIP content, the maximal decline in the number of anterior pituitary VIP binding sites was achieved by Day 2 of oPRL administration. Hypothalamic GnRH-I content decreased after 2 days of oPRL injection and remained low through Day 14 of the experiment. GnRH-II levels declined with time, reaching significantly lower levels after 8 days of injections, and remained low through Day 14. Plasma LH levels also declined (p < 0.05) after Day 14 of oPRL administration. In experiment 2, two groups (n = 6) of incubating birds were used: controls receiving injections of vehicle only and birds receiving injections of oPRL (4 mg/bird/day) for 10 days. Exogenous oPRL had no effect on hypothalamic VIP, GnRH-I or II, anterior pituitary VIP binding sites, or plasma turkey PRL or LH. The findings suggest that in laying hens, PRL inhibits its own secretion by acting on both the hypothalamus and the anterior pituitary; this phenomenon does not occur in incubating birds. Furthermore, we provide evidence that PRL acts centrally to reduce LH levels by reducing GnRH levels in the hypothalamus.
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U2 - 10.1095/biolreprod48.6.1246
DO - 10.1095/biolreprod48.6.1246
M3 - Article
C2 - 8391330
AN - SCOPUS:0027258787
SN - 0006-3363
VL - 48
SP - 1246
EP - 1250
JO - Biology of reproduction
JF - Biology of reproduction
IS - 6
ER -