Seasonal alterations in circadian melatonin rhythms of the European wild boar and domestic gilt

The aims of the present study were: 1) to determine if the European wild bo ar exhibits a circadian pattern of melatonin secretion under its natural li ght environment; 2) to compare this pattern with the pattern in domestic pi gs reared under the light environment typical for domesticity; and 3) to de termine if there are seasonal alterations in melatonin rhythms. Four to six young, pure-bred, European wild boars and four to six cross-bred (Yorkshir e x Finnish Landrace) domestic gilts were sampled at 2-hr intervals for 48 hr at the spring/autumn equinoxes and summer/winter solstices. Samples were obtained via saphenous arterial catheters from the wild boats and via car vein catheters from the domestic gilts. The ambient light intensity was rec orded simultaneously with sampling both outdoors and indoors. Following eth er extraction, the serum samples were assayed for melatonin using a commerc ial RIA (Buhlman(R)). All the experimental animals exhibited a distinct cir cadian pattern in melatonin secretion, with high concentrations occurring d uring the scotophase. There was no difference in scotophase melatonin respo nse between the wild boars and domestic gilts in any season ill terms of me an melatonin concentration or peak value. The mean duration of increased me latonin secretion (more than two standard deviations over a mean photophase concentration) in 24 hr. in the wild boars in spring, summer, autumn and w inter, was 10, 6, 11 and 17 hr, respectively, and in the domestic gilts, 9, 8, 12 and 11 hr, respectively. These results demonstrate the existence of circadian rhythm in melatonin secretion in both the European wild boar and domestic pig. In both groups, the duration of secretion is subject to seaso nal alterations. The results suggest no difference in photoperiodic-melaton in transduction between the European wild boar and domestic pig whether due to altered genotype or reduced light environment.