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

Abstract

To clarify the role of serotonin (5-HT) in the regulatory mechanism of L-tryptophan (TRP)--induced growth hormone (GH) secretion in cattle, changes in 5-HT concentrations in the cerebrospinal fluid (CSF) in the third ventricle (3V) and GH in plasma before and after the peripheral infusion of TRP were determined simultaneously. The direct effect of TRP on GH release from the dispersed anterior pituitary cells was also assessed. A chronic cannula was placed in 3V by stereotaxic surgery, then CSF and blood were withdrawn under physiological conditions. TRP (38.5 mg/kg BW) was infused through an intravenous catheter from 12.00 to 14.00 hours and CSF and blood sampling were performed from 11.00 to 18.00 hours at 1-h intervals. The concentration of 5-HT in CSF was determined by high-performance liquid chromatography with electrochemical detection. GH, melatonin (MEL), and cortisol (CORT) concentrations were measured by radio-immunoassay and enzyme-immunoassay. Concentrations of 5-HT were increased by TRP infusion. The TRP infusion significantly increased GH release. On the other hand, TRP did not stimulate GH release from the bovine pituitary cells. MEL and CORT concentrations were not altered by TRP infusion. These results suggest that TRP induced GH release via the activation of serotonergic neurons in cattle.

Increasing serotonin concentrations alter calcium and energy metabolism in dairy cows

“…Metabolites in the serotonergic pathway have been previously administered in several species to characterize various physiological responses. Particularly in bovines, serotonin was administered to calves to characterize their cardiovascular and pulmonary responses (Linden et al 1993(Linden et al , 1996, and L-tryptophan was administered to steers to evaluate the effects on growth hormone secretion in cattle (Kasuya et al 2010). However, to our knowledge, the present study is the first in which 5-HTP was administered to lactating dairy cows.…”

L‐DOPA attenuates prolactin secretion in response to isolation stress in Holstein steers

“…This technique was based on our previous report describing the measurement of serotonin concentrations in CSF after peripheral application of a serotonin precursor in steers (Kasuya et al . ). As expected, L‐DOPA treatment significantly increased DA levels, suggesting that the peripheral supply of the precursor (L‐DOPA) reached the CNS and augmented synthesis of its product (DA).…”

“…DA concentrations in CSF were determined using HPLC with electrochemical detection (HTEC500 System; Eicom, Kyoto, Japan) based on a method previously described (Ago & Matsuda ; Kasuya et al . ). DA was separated using an Eicompak PP‐ODS column (30 × 4.6 mm; Eicom) at 25°C.…”

“…Japan) based on a method previously described (Ago & Matsuda 2003;Kasuya et al 2010). DA was separated using an Eicompak PP-ODS column (30 ¥ 4.6 mm; Eicom) at 25°C.…”

Twenty-four-hour profiles of metabolic and stress hormones in sheep selected for a calm or nervous temperament

“…Therefore, it is possible that, as with cortisol, prolactin secretion will differ between the temperament groups only during exposure to a stressor; however, no study to date has looked at prolactin concentrations in these sheep. This concept is supported by a study in heifers where behavioral reactivity to stressors was correlated with the prolactin response to those stressors but not with concentrations of prolactin at rest [61]. In contrast to our findings, in both the high anxiety and/or low anxiety and Maudsley reactive and nonreactive models, the line of rats that appear more disturbed by stressors have greater plasma concentrations of prolactin at rest than rats that are less disturbed, in the absence of any differences in corticosterone or ACTH [41,62,63].…”