No abstract

Plasma melatonin concentrations were measured every 1-2 h over 24 h and plasma luteinizing hormone (LH) concentrations every 15 min over 12 h in domestic gilts reared under artificial light regimens that had previously been used to demonstrate photoperiodic effects on puberty. In Expt 1, the light regimens both commenced at 12 h light: 12 h dark (12L:12D) and either increased (long-day) or decreased (short-day) by 15 min/week until the long-day gilts were receiving 16L:8D and the short-day gilts 8L:16D at sampling. In Expt 2, both light regimens commenced at 12L:12D and either increased (long-day) or decreased (short-day) by 10 or 15 min/week to a maximum of 14.5L:9.5D or a minimum of 9.5L:14.5D before being reversed. Sampling took place when daylength had returned to 14L:10D (long-day) or 10L:14D (short-day). In immature gilts housed at 12L:12D (Expt 1) and in postpubertal (Expt 1) and prepubertal (Expt 2) gilts reared under long-day or short-day light regimens, mean plasma melatonin concentrations were basal (3.6 pg/ml) when the lights were on and increased to peak concentrations greater than 15 pg/ml within 1-2 h after dark, before declining gradually to basal concentrations at or near the end of the dark phase. In prepubertal gilts bearing subcutaneous melatonin implants and reared under long-days (Expt 2), mean plasma melatonin concentration in the 6 h before dark was 91.9 +/- 5.26 pg/ml and 125.0 +/- 6.66 pg/ml 1 h after dark, but this increase was not statistically significant. In Expt 2, the short-day gilts had fewer LH pulses (2.6 +/- 0.25 vs. 4.6 +/- 0.24; P less than 0.01) in the 12-h sampling period than the long-day gilts, but the amplitude of the pulses (2.28 +/- 0.23 vs. 1.26 +/- 0.16 ng/ml; P less than 0.01) and the area under the LH curve (78.8 +/- 5.60 vs. 47.3 +/- 6.16; P less than 0.01) was greater in the short-day gilts. In the short-day, but not in the long-day, gilts LH pulses were more frequent (2.0 +/- 0.0 vs. 0.6 +/- 0.25; P less than 0.01), but had a smaller area (61.9 +/- 7.2 vs. 120.2 +/- 23.6; P less than 0.05) in the 6 h of dark than in the 6 h of light, which together made up the 12-h sampling period.(ABSTRACT TRUNCATED AT 400 WORDS)

—Rat brain contains the enzyme which forms sulphate conjugates of phenols, phenolsulphotransferase (EC 2.8.2.1), but the physiological role of the enzyme is unclear. The enzyme is unevenly distributed in rat brain, with the activity 13 times higher in the hypothalamus than in the cerebellum. Phenolsulphotransferase does not seem to be primarily located in glial cells. Cultured cells (type C6 astrocytoma) derived from rat glia had less than 1 per cent of the phenolsulphotransferase activity of whole rat brain. Sulphate conjugation of neutral compounds may be important in their removal from brain. The pineal and pituitary glands, areas outside the blood‐brain barrier had very low phenolsulphotransferase activity. The activity of the enzyme in brain varied widely among different species: rabbit and rat had much higher levels of activity than mouse or frog; the activity in human brain was intermediate. Phenolsulphotransferase also occurred in other organs, including liver, heart, testes, lung, spleen, salivary glands, and intact or decentralized superior cervical ganglion. There was no correlation of enzyme activity with adrenergic or cholinergic innervation, or with the known roles of various tissues in drug metabolism or detoxification. The enzyme activity does not seem to be under neuronal control since ganglionectomy did not affect the phenolsulphotransferase activity of salivary glands. The precise localization of phenolsulphotransferase remains to be established, as well as the physiological importance of sulphate conjugation of phenols in brain and other organs.