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To understand the regulatory mechanism of the secretory rhythm of GH and the involvement of melatonin (MEL) in GH regulation in cattle, daytime and nighttime profiles of GH secretion and the effect of a photic stimulation on nocturnal GH and MEL secretion were investigated in Holstein steers. Steers were kept under a constant lighting condition of 12 h of light (LIGHT; 500 lx, 0600 to 1800 h):12 h of dark (DARK; 10 lx, 1800 to 0600 h). In Exp. 1, blood was taken for 4 h at 15-mm intervals during LIGHT (1100 to 1500 h) and DARK (2300 to 0300 h), respectively. The sampling was also performed from 0500 to 0900 h, with the usual light transition (light onset at 0600 h; morning sampling). In Exp. 2, steers were exposed to light (500 lx) for 1 h from 0000 to 0100 h. Plasma GH and MEL concentrations were determined by RIA and enzyme immunoassay, respectively. Both GH (P <0.05) and MEL (P < 0.01) concentrations in plasma for 4 h during DARK were greater than those during LIGHT. On the other hand, although MEL concentrations were decreased after the light onset at 0600 during the morning, GH release was not altered. Increased GH secretion during DARK was suppressed (P < 0.01) by the 1 h of light exposure, as were MEL concentrations (P < 0.05). Pineal MEL, which was affected by the photic condition, may play an important role in the secretory rhythm of GH secretion in cattle. [ABSTRACT FROM AUTHOR]

The effects of dietary sucrose on the metabolic rate of plasma glucose and ruminal propionate as well as the change in nitrogen kinetics were examined in four mature wethers fitted with rumen fistulas in Tsukuba, Japan in 1990. Wethers were fed at 12 equal intervals daily on crushed lucerne hay cubes (1233 g DM/day), with or without 204 g/day of sucrose. Plasma urea and glucose kinetics were determined following a single intravenous injection of [I5N]urea and [U-13C]glucose respectively; and the kinetics of ruminal ammonia and propionate were determined following a single intraruminal injection of [15N]ammonium chloride and [2–13c]sodium propionate respectively. Following supplementation of sucrose to the diet, nitrogen retention was increased (P < 0·05) with a decrease in plasma urea concentration (P < 0·05) and urinary urea excretion (P < 0·05). Sucrose supplementation decreased (P < 005) the concentration and irreversible loss rate of ruminal ammonia. Urinary allantoin excretion did not change with sucrose treatment, but the flow rate of non-ammonia-nitrogen from the rumen was increased P < 0·05). The transfer rate of ruminal ammonia to plasma urea was also decreased (P < 0·01), whilst the transfer rate of plasma urea to ruminal ammonia was increased (P < 0·05) by dietary sucrose. Sucrose supplementation resulted in a higher concentration of propionate and butyrate (P < 0·05) in the rumen with no significant change in acetate or pH. The concentration of plasma glucose did not change with sucrose treatment, but the concentration of insulin, pool size (P < 0·05) and the irreversible loss rate of glucose (P < 0·01) were increased, reflecting the increase in the production rate of ruminal propionate (P < 0·05). It was concluded that the supplementation of sucrose affected the metabolism of urea and glucose in plasma via a change in ruminal production rate of ammonia and propionate, respectively. [ABSTRACT FROM PUBLISHER]

The effects of sucrose supplementation on nitrogen kinetics and energy metabolism were examined in sheep fed lucerne hay cubes using a 15N isotope dilution method and balance and respiration trials in Tsukuba, Japan in 1988. Sheep were fed lucerne hay cubes (1183 g DM/day), with or without 204 g/day sucrose, at 2 h intervals from continuous feeders. Supplementation with sucrose decreased urinary N excretion (P < 0·01), resulting in an increase in N retention from – 1·1 to + 2·0 g N/day (P < 0·01). Supplementation with sucrose resulted in no change in faeces and methane energy, a decrease in urinary energy (P < 0·01) and an increase in heat production and energy balance (P < 0·01). Sucrose supplementation also resulted in lower rumen ammonia (P < 0·05) and plasma urea concentrations (P < 0·05) and reduced urinary urea excretion (P < 0·01). The fermentation of sucrose in the rumen resulted in a decrease in rumen pH (P < 0·01) and in the acetate: propionate ratio (P < 0·05). Sucrose supplementation increased the proportion of urea transferred to the rumen (P < 0·05), non-ammonia N (NAN) concentration in the rumen (P < 0·001) and NAN flow from the rumen to the lower digestive tract (P < 0·001). Urinary allantoin excretion rate increased with sucrose supplementation (P < 0·05). The plasma glucose concentration was unchanged but plasma insulin concentration was increased with sucrose supplementation (P < 0·05). The influence of energy-rich supplements, such as sucrose, on N kinetics and the mechanism of the increase in N retention with sucrose supplementation are discussed. [ABSTRACT FROM PUBLISHER]

Abstract: The aims of the present study were to determine whether salsolinol (SAL), a dopamine-related compound, is present in the bovine posterior pituitary (PP) gland, and to clarify the effect of SAL on the secretion of prolactin (PRL) in ruminants. SAL was detected in extract of bovine PP gland using high-pressure liquid chromatography with electrochemical detection (HPLC-EC). A single intravenous (i.v.) injection of SAL (5 and 10mg/kg body weight) significantly and dose-dependently stimulated the release of PRL in goats (P <0.05). Plasma PRL levels reached a peak 10min after the injection, then gradually returned to basal values in 60–80min. The PRL-releasing pattern was similar to that in response to sulpiride (a dopamine receptor antagonist). The intracerebroventricular (i.c.v.) injection of 1mg of SAL had no significant effect on the release of PRL in calves, however, 5mg significantly stimulated the release (P <0.05) with peak values reached 30–40min after the injection. Moreover, SAL significantly stimulated the release of PRL from cultured bovine anterior pituitary cells at doses of 10−6 and 10−5 M, compared to control cells (P <0.05). Taken together, our data clearly show that SAL is present in extract of the PP gland of ruminants, and has PRL-releasing activity both in vivo and in vitro. Therefore, this endogenous compound is a strong candidate for the factor having PRL-releasing activity that has been previously detected in extract of the bovine PP gland. [Copyright &y& Elsevier]