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M. C. Macnamee and P. J. Sharp

ABSTRACT

An assessment was made of the possible role of hypothalamic dopamine in the regulation of changes in plasma prolactin and LH in laying and broody bantam hens. Specific dopamine-binding sites were identified, using [3H]domperidone, in the anterior pituitary gland and in the anterior and posterior hypothalamus. The mean concentrations of dopamine-binding sites in both parts of the hypothalamus were 59–66 fmol/mg protein and did not differ between laying and incubating hens. The concentration of dopamine binding sites in the anterior pituitary gland was significantly (P<0·001) greater in laying than in incubating hens (278 ± 46 compared with 420 ± 32 fmol/mg protein, n = 5).

The turnover rates of dopamine were compared in the anterior and posterior hypothalami of laying, incubating and nest-deprived hens. The turnover rates were estimated from the rate of accumulation of dopamine after inhibiting its catabolism using the monoamine oxidase inhibitor, pargyline, or by measuring the ratio of the concentrations of dopamine and its major metabolite, homovanillic acid. Both methods gave the same results. The turnover of dopamine was increased in the anterior but not posterior hypothalamus of incubating hens when compared with laying or nest-deprived hens.

These results show, for the first time in birds, that the anterior pituitary gland contains specific binding sites for dopamine and that the concentration of these binding sites is inversely related to the concentration of plasma prolactin. The marked increase in dopaminergic activity in the anterior hypothalamus of incubating hens may stimulate the release of unidentified prolactin-releasing factors and/or inhibit the release of LH by exerting an inhibitory influence in the area of the hypothalamus containing LHRH cell bodies.

Journal of Endocrinology (1989) 121, 67–74

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M. C. Macnamee and P. J. Sharp

ABSTRACT

An assessment was made of the possible role of hypothalamic 5-hydroxytryptamine (5-HT) in the regulation of prolactin secretion in broody bantam hens. Prolactin secretion was stimulated less in incubating hens deprived of their nests for 24 h (nest-deprived) than in laying hens after administration of the 5-HT receptor agonist quipazine, or precursor 5-hydroxytryptophan. One type of 5-HT-binding site was found in the anterior and posterior hypothalami of out-of-lay, incubating and laying hens. Differences in prolactin secretion in these birds could not be accounted for by changes in the abundance of this type of 5-HT-binding site. Another type of 5-HT-binding site, with a higher density but lower affinity, was found in the anterior hypothalami of laying hens. No specific 5-HT-binding sites were found in the anterior pituitary gland.

The turnover rates of 5-HT were compared in the anterior and posterior hypothalami of laying, incubating and nest-deprived hens. The turnover rates were estimated from the rate of accumulation of 5-HT after inhibiting its catabolism using the monoamine oxidase inhibitor, pargyline, or by measuring the ratio of the concentrations of 5-HT and its major metabolite, 5-hydroxyindole acetic acid. Both methods of measurement gave the same results. The turnover of 5-HT was increased in the anterior but not posterior hypothalami of incubating hens when compared with laying or nest-deprived hens. There was also a significant increase in turnover of 5-HT in the posterior hypothalami in nest-deprived hens when compared with laying or incubating birds.

These results demonstrate a strong correlation between the function of 5-HT neurones in the hypothalamus and reproductive activity. They are consistent with the view that hypothalamic 5-HT is involved in the regulation of prolactin secretion.

Journal of Endocrinology (1989) 120, 125–134

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P. J. Sharp, M. C. Macnamee, R. J. Sterling, R. W. Lea, and H. C. Pedersen

ABSTRACT

The interactions between broody behaviour and changes in concentrations of plasma prolactin and LH were investigated in bantam hens. Adoption of newly hatched chicks caused incubating hens to leave their nests and prevented plasma prolactin decreasing as rapidly as in hens deprived of their nests and not given chicks. Further, the hens allowed to rear chicks came back into lay later (P< 0·001) than the hens not allowed chicks. Plasma prolactin decreased and plasma LH increased in hens deprived of their nests: these changes were reversed when the hens re-nested. The changes in plasma LH and prolactin in nest-deprived and re-nesting birds were not always synchronous; this was particularly clear immediately after nest deprivation when the increase in plasma LH preceded the decrease in the plasma prolactin. Readiness to incubate disappeared between 48 and 72 h after nest deprivation and corresponded with the time when plasma prolactin decreased to baseline values. Administration of ovine prolactin depressed (P<0·01) the initial increase in plasma LH after nest deprivation, but repeated administration of prolactin for up to 72 h failed to suppress plasma LH to the values found in incubating hens. Repeated administration of ovine prolactin at 5- to 8-h intervals for 72 h maintained readiness to incubate in nest-deprived hens. It is concluded that the secretion of prolactin in broody hens is facilitated by the presence of chicks and that increased concentrations of plasma prolactin maintain incubation behaviour. In incubating hens the secretion of LH and prolactin may be partly regulated independently. In addition, LH secretion may also be inhibited by increased plasma prolactin.

J. Endocr. (1988) 118, 279–286