Abstract 1. Furazolidone or nitrofurazone were given orally to laying turkeys at doses of 7.5, 15 or 30 mg/kg for 7 d. Plasma concentrations of luteinising hormone (LH), prolactin (PRL) and egg production were measured before, during and after treatment. 2. Both drugs produced dose‐dependent decreases in LH concentration which were statistically significant at doses of 15 and 30 mg/kg. Plasma PRL concentration was significantly increased in birds receiving 15 or 30 mg/kg of nitrofurazone, and tended to increase in the other treated groups, but this was not statistically significant. 3. Egg production was lowered in a dose‐dependent manner by both drugs. However, nitrofurazone appeared to be more potent in reducing egg production than furazolidone. 4. Birds given 15 mg/kg of either drug were injected intramuscularly with luteinising hormone releasing hormone (LHRH) at a dose of 5 μg/kg and blood was collected immediately before and 30 min after LHRH administration. 5. Nitrofurazone significantly reduced the rise in LH induced by LHRH. Seven days after withdrawing the drug, the LHRH‐induced LH release was not significantly different when compared to that in the control group or that seen on day 7 of treatment. Notes This is Scientific Journal Series paper 15,414 of the Minnesota Agricultural Experiment Station. Present address: Department of Veterinary Medicine, Pharmacology and Toxicology, Faculty of Veterinary Science, University of Kartoum, PO Box 32, Khartoum North, Sudan.
Vasoactive intestinal peptide (VIP) stimulates prolactin (PRL) secretion. Ovine PRL induces incubation behavior in avian species. This study was designed to determine whether VIP can elevate plasma PRL for up to 3 h. Saline or porcine VIP (pVIP; 30, 60, or 150 ng/min) was infused into the median eminence of laying turkeys for 1 h. The 60- and 150-ng doses of pVIP increased plasma PRL (p < 0.01), whereas the 30-ng dose was insignificant. Pituitary PRL content decreased in pVIP-treated turkeys. Two-hour infusion of 60 or 150 ng chicken VIP (cVIP)/min produced similar elevations of plasma PRL (p < 0.001), which declined within 80 min. Both treatments induced insignificant increases in pituitary PRL mRNA. Saline or cVIP (30, 60, or 60 [pulsed] ng/min) was infused into the median eminence for 3 h. Sixty ng cVIP/min induced the largest PRL release (p < 0.05). The pulsatile and low-cVIP treatments resulted in release of a significant amount of PRL in comparison to the saline treatment (p < 0.01). All cVIP treatments resulted in decreased pituitary PRL content (p < 0.05). The 60-ng dose increased PRL mRNA (p < 0.1). This study shows that 60 ng VIP/min causes the maximum PRL release in laying turkeys. However, pituitary PRL content is depleted and PRL synthesis cannot maintain PRL secretion at high levels.
Vasoactive intestinal peptide (VIP) is a hypothalamic prolactin (PRL)-releasing factor in the turkey. The hypothesis in the present study was that active immunization of turkeys with VIP would neutralize endogenous VIP, decrease circulating PRI, and consequently prevent the expression of incubation behavior. Large white female turkeys were divided into three experimental groups comprising untreated controls, control turkeys immunized with keyhole limpet hemocyanin (KLH), and turkeys immunized with synthetic chicken VIP conjugate (KLH-cVIP). Each turkey received four injections at 4-wk intervals, starting on the day of photostimulation. The immune response, measured by the percentage binding of monoiodinated chicken VIP (cVIP) to plasma at a dilution of 1:1000, averaged 11.8 +/- 2.5% during the reproductive life cycle. Immunization against KLH-cVIP prevented the normal increases of PRL that are associated with the photo-induced reproductive cycle. Over a 21-wk period beginning at photostimulation, KLH-cVIP-immunized birds exhibited a maximal plasma PRL level of 82.2 +/- 29.5 ng/ml, compared to 367.7 +/- 66.6 ng/ml and 227.5 +/- 51.7 ng/ml for non- and KLH-immunized turkeys, respectively. The total number of nest visits per hen during the 147-day experimental period decreased from 320.0 +/- 48.2 in the nonimmunized controls to 180.7 +/- 53.7 and 149.4 +/- 13.1 visits in KLH- and KLH-cVIP conjugate-immunized turkeys. Turkeys that showed an immune response to KLH-cVIP immunization did not exhibit incubation behavior, whereas 54% and 33% of non- and KLH-immunized hens incubated their eggs.(ABSTRACT TRUNCATED AT 250 WORDS)
An inverse relationship often exists between prolactin (Prl) and LH in avian species. Our study was designed to investigate the relationship between hypothalamic and posterior pituitary vasoactive intestinal peptide (VIP)—an endogenous Prl-releasing peptide—and chicken GnRH-I and GnRH-II. Hypothalamic VIP content was increased after photostimulation, reaching its highest levels in incubating and photorefractory birds. The highest hypothalamic GnRH-I content was in laying hens followed by that in photostimulated and incubating birds. The lowest levels were in the nonphotostimulated birds. Hypothalamic GnRH-II increased after photostimulation, then fell to nonphotostimulated levels during incubation and photorefractoriness. Posterior pituitary VIP content was elevated in response to photostimulation, reaching a peak value in the laying and incubating birds, then declining in the photorefractory hens. Posterior pituitary GnRH-I and GnRH-II content peaked in the incubating birds. Ovariectomy caused a significant reduction in hypothalamic GnRH-I and GnRH-II with no effect on VIP; no changes were found in the posterior pituitary due to ovariectomy. Reducing day length caused a significant decrease in the hypothalamic and the posterior pituitary content of VIP and GnRH-I, and GnRH-II. Ovine Prl (oPrl) administration to laying hens reduced the hypothalamic VIP and GnRH-I and GnRh-II content. Posterior pituitary GnRH-I content was also reduced. Although GnRH-II levels were reduced by Day 4 of injections, they rose to peak levels by Day 14 of oPrl administration. Posterior pituitary VIP content was not altered by oPrl.
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