title: Concentrations of plasma melatonin and luteinizing hormone in domestic gilts reared under artificial long or short days.
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)
authors.affiliation: Animal Production Division, Department of Agriculture, South Perth, Australia.
authors.forename: A M
authors.initials: AM
authors.lastname: Paterson
authors.forename: G B
authors.initials: GB
authors.lastname: Martin
authors.forename: A
authors.initials: A
authors.lastname: Foldes
authors.forename: C A
authors.initials: CA
authors.lastname: Maxwell
authors.forename: G P
authors.initials: GP
authors.lastname: Pearce
mesh_terms: D000818:Animals; D005260:Female; D008027:Light; D007986:Luteinizing Hormone / Q000097:blood*; D008550:Melatonin / Q000097:blood*; D010507:Periodicity; D011863:Radioimmunoassay; D013552:Swine / Q000097:blood*
chemical_list: D007986:Luteinizing Hormone; D008550:Melatonin