title: Sensitivity of goats to a light pulse during the night as assessed by suppression of melatonin concentrations in the plasma.
abstract: This study investigates the ability of a 1 h light pulse of different intensities at night to suppress plasma melatonin in goats. Six female Saanen dairy goats, about 2 yr old, were housed in a light-tight shed. The goats were habituated for 1 wk to an 8L:16D photoperiod (40.70 +/- 4.16 microW/cm2; 137 +/- 14 lux), lights on 0800 h. A 1 h light pulse, of different intensity on each occasion, was given from 1900 to 2000 h. Light intensity was measured by using a lux meter (mean of 36 measurements at goat's eye level). Five different light intensities were given during December in the order 4.22 +/- 0.62 microW/cm2 (14.2 +/- 2.1 lux), 0.68 +/- 0.09 microW/cm2 (2.3 +/- 0.3 lux), 0.26 +/- 0.004 microW/cm2 (0.87 +/- 0.14 lux), darkness, 40.70 +/- 4.16 microW/cm2 (137 +/- 14 lux), with 1-3 d between treatments. The goats were bled hourly from 1500 to 1900 h and every 15 min from 1900 to 2100 h, and a last bleed occurred at 2200 h. Dark-phase samples were taken in dim red light (less than 0.03 microW/cm2; 0.1 lux). Plasma was assayed for melatonin by radioimmunoassay. Suppression of melatonin concentrations increased as light intensity increased as follows: Darkness, 0%; 0.26 +/- 0.004 microW/cm2; 0%; 0.68 +/- 0.09 microW/cm2; 43.1%; 4.22 +/- 0.62 microW/cm2, 71.1%; 40.70 +/- 4.16 microW/cm2, 81.2%. Suppression was significant (P less than 0.05) at light intensities greater than 0.68 microW/cm2, 2.3 lux. A hyperbolic relationship existed between percent suppression and light intensities.
authors.affiliation: Department of Biochemistry, University of Surrey, Guildford, U.K.
authors.forename: S L
authors.initials: SL
authors.lastname: Deveson
authors.forename: J
authors.initials: J
authors.lastname: Arendt
authors.forename: I A
authors.initials: IA
authors.lastname: Forsyth
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002940:Circadian Rhythm / Q000528:radiation effects*; D003624:Darkness; D005260:Female; D006041:Goats / Q000378:metabolism*; D008027:Light; D008550:Melatonin / Q000097:blood*; D010870:Pineal Gland / Q000378:metabolism / Q000528:radiation effects; D011863:Radioimmunoassay
chemical_list: D008550:Melatonin