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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-min 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. Key words: cattle, growth hormone, melatonin, photic stimulation, rhythm

The objective of this study was to investigate the presence of tumor necrosis factor-[alpha] (TNF-[alpha]) in the central nervous system and the effects of lipopolysaccharide on central and peripheral concentrations of TNF-[alpha], behavioral conditions (standing or lying), elimination scores (defecation or urination), rectal temperature, and food intake (as-fed basis) in Chinese Meishan pigs. Intravenous injections of lipopolysaccharide resulted in increased (P < 0.05) plasma concentrations of TNF-[alpha] and cortisol. Although urination was not alfected by the administration of lipopolysaccharide, defecation was stimulated (P < 0.05). Lipopolysaccharide increased (P < 0.05) rectal temperature and standing rate, and inhibited (P < 0.05) food intake in pigs. To determine whether TNF-[alpha] is present in the porcine central nervous system as well as in peripheral blood, TNF-[alpha] and its specific transcripts in brain tissues (hypothalamus, amygdala, or hippocampus) and the pituitary were determined. The abundance of TNF-[alpha] messenger RNA and immunoreactive TNF-[alpha] were observed in all tissues, and the concentrations of TNF-[alpha] were increased (P < 0.05) by the intramuscular injection of lipopolysaccharide. These results suggest that TNF-[alpha] is present in the central nervous system, and plays some roles in its biological regulation in Chinese Meishan pigs. Key Words: Brain, Lipopolysaccharides, Meishan, Pigs, Pituitary, Tumor Necrosis Factor