Effects of serotonin injected into the third ventricle on prolactin and growth hormone secretion in Holstein steers

Abstract

In order to clarify the role of serotonin (5‐HT) in the regulation of pituitary hormones, the effects of 5‐HT injected into the third ventricle (3V) on prolactin (PRL) and growth hormone (GH) release were investigated in Holstein steers. A chronic cannula was implanted in 3V by stereotaxic surgery under general anesthesia. After sufficient recovery from surgery, 5‐HT (0, 0.1, 1.0, 2.0 mg) was injected into via the cannula and blood samples were collected over 4 h. Plasma PRL and GH concentrations were determined by radioimmunoassay. PRL release was significantly stimulated by the injection of 5‐HT. The increase in PRL was observed at 20 min after the injection at three doses and the highest dose (2.0 mg) was the most effective in stimulating PRL release. The injection of 5‐HT into 3V, at all doses tested, did not alter GH release significantly. Our results suggest that 5‐HT is involved in the regulation of PRL release partly through the hypothalamus in cattle.

A possible role of central serotonin in L‐tryptophan‐induced GH secretion in cattle

“…Although the stimulatory effect of 5-HT on GH secretion has been reported, a recent experiment in our laboratory in which 5-HT was injected into the 3V of Holstein steers did not show an apparent elevation of GH secretion (Kasuya et al 2008). The relationship between 5-HT in the CNS and the hypothalamopituitary-adrenal (HPA) axis, including secretion of glucocorticoids from the adrenal cortex, may explain the discrepancy in these results.…”

“…Although the stimulatory effect of 5‐HT on GH secretion has been reported, a recent experiment in our laboratory in which 5‐HT was injected into the 3V of Holstein steers did not show an apparent elevation of GH secretion (Kasuya et al. 2008).…”

“…1995). However, the injection of 5‐HT into the third ventricle (3V) did not alter GH secretion in steers (Kasuya et al. 2008).…”

“…In cattle, quipazine, a nonselective serotonin agonist, stimulated GH release when it was administered peripherally (Sartin et al 1987;Gaynor et al 1995). However, the injection of 5-HT into the third ventricle (3V) did not alter GH secretion in steers (Kasuya et al 2008). Therefore, the mechanism underlying the effect of the serotonergic system on GH release in this species remains to be clarified.…”

Secretory pattern and regulatory mechanism of growth hormone in cattle

“…We have developed a stereotaxic apparatus designed for cattle (Saito et al 2004) enabling us to approach a specific brain area, in particular the hypothalamus and its vicinities (Hashizume & Kasuya 2009). The technique is useful for the experiments described below: push-pull perfusion in the median eminence to measure the concentrations of GHRH and SS (Kasuya et al 2005), intraventricular injection of various candidates playing an important role in the regulation of GH secretion to evaluate their effects on GH secretion via the hypothalamus (Kasuya, et al 2006(Kasuya, et al , 2008b and frequent CSF sampling to measure the concentrations of neurotransmitters considered as regulators of GH secretion (Kasuya et al 2010).…”