Influence of lighting cycles on daily rhythms in concentrations of plasma tri-iodothyronine and thyroxine in intact and pinealectomized immature broiler hens (Gallus domesticus)

Abstract

The effects of pinealectomy on the daily rhythms of concentrations of tri-iodothyronine (T3) and thyroxine (T4) were investigated in sexually immature female chickens exposed to 21-, 24- and 27-h cycles of light and darkness, or to extended periods of light or darkness for more than 24 h. In pinealectomized and control birds, rhythms in levels of plasma T3 and T4 were entrained by all lighting cycles and decreased in amplitude or disappeared in continuous light or darkness. In pinealectomized and control birds held on 21-h (11 h light:10 h darkness; 11L:10D) and 24-h (14L:10D) lighting cycles, the peak of the T4 rhythm coincided with, or lagged, the trough in the rhythm of T3 while in birds held on a 27-h (14L:13D) lighting cycle, the peak of the T4 rhythm preceded the trough in the rhythm of T3. Pinealectomy resulted in significant effects on the phases or amplitudes of rhythms of T3 or T4 in all lighting schedules except 4L:20D. However, these effects were not consistent in direction between experimental groups and were, therefore, of doubtful physiological significance. Pinealectomy increased the mean level of plasma T4 in birds exposed to continuous light or darkness or to 4L:20D. A corresponding reduction in mean levels of plasma T3 was seen in birds exposed to continuous light or darkness. It is concluded that under the lighting conditions investigated pinealectomy had no clear effect on the phases or amplitude of daily rhythms of levels of T4 or T3. However, after the effects of the feeding pattern on thyroid hormone rhythms imposed by the lighting cycle were removed by placing birds in constant lighting conditions, pinealectomy appeared to exert an inhibitory action on thyroid function.

Seasonal variations of in vivo and in vitro melatonin production in a passeriform bird, the house sparrow (Passer domesticus)

“…Pinealectomized mammals are no longer able to respond to changing photoperiod, but seasonality can be restored by appropriate administration of exogenous melatonin [Hastings et al, 1985;Bartness et al, 1993;Goldman, 1999]. Based on a large number of such studies in mammals, photoperiodism experiments in birds focussed on pinealectomy, [Siopes and Underwood, 1987;Sharp et al, 1984;Pant and Chandola-Saklani, 1992], continuous melatonin administration via implants [John et al, 1986], or the manipulation of the duration of the melatonin signal [Juss et al, 1993]. No consistent effects of pinealectomy on the annual cycles of reproduction have yet been found in birds [Gwinner et al, 1981;Simpson et al, 1983;Follett et al, 1985].…”

Plasma Thyroid Hormone Concentrations in a Wintering Passerine Bird: Their Relationship to Geographic Variation, Environmental Factors, Metabolic Rate, and Body Fat

“…Changes in the activity of the thyroid system in response to environmental stimuli are complex and probably involve changes in thyroid gland output, peripheral conversion of T 4 to T 3 , degradation of T 3 , modulation of TH by plasma binding proteins, and regulation of cellular TH receptors (Rudas andPethes 1984, 1986;McNabb 1992;Darras et al 1995). Natural rhythms in plasma concentrations of THs occur seasonally and daily, probably in response to cold exposure and food intake (Kühn and Nouwen 1978;May 1978;Chandola and Pathak 1980;Klandorf et al 1981;Sharp et al 1984;May and Reece 1986;Stokkan et al 1985;Cogburn and Freeman 1987). Food restriction and nutritional status also affect circulating concentrations of TH (Harvey et al 1981;Klandorf and Harvey 1985;Eales 1988).…”

Improvements in the determination of the turnover rate of plasma thyroxine in avian species: application to the Japanese quail

“…Bobek et al (1980) showed that when four successive blood samples were taken from Japanese quail over a 12-h period the T4 concentration dropped by approximately 20%. It is difficult to ascertain the contribution that stress has on this decrease as the natural daily rhythm in the T4 concentration in the chick shows fluctuations of similar magnitude (Sharp, Klandorf & Lea, 1984). Previous work on T4 turn¬ over in quail has suggested that a sampling time of 3-12 h after the i.v.…”