Absence of a nocturnal rise in either norepinephrine, N-acetyltransferase, hydroxyindole-O-methyltransferase or melatonin in the pineal gland of the domestic pig kept under natural environment photoperiods

Abstract

Castrated male and intact female pigs were kept under natural photoperiodic and temperature condi tions and were killed over a 24 h period in either May (under long days) or in December (under short days). Neither the pineal norepinephrine (NE) concentration nor the melatonin content rose at night: like wise, neither the activities of N-acetyltransferase (NAT) nor hydroxyindole-O-methyltransferasc (HIOMT) increased during darkness. In May pineal melatonin content actually decreased (P<0.05) at night while in December NAT activity fell (P < 0.05) at night. Daytime levels of each of these variables were equivalent to those measured in other species. The absence of a nocturnal increase in pineal melato nin production in either Mayor December raises the possibility that pineal melatonin may be involved in regulating seasonal breeding in the pig in a manner different from other mammals. Alternatively, pineal melatonin production may be unrelated to seasonal reproduction in the pig.Few reports have examined levels of melatonin in the blood of the wild boar and domestic pig. Kennaway et al. [8] measured melatonin in the plasma of one boar and found that the midnight level was about 3 times higher than the midday value. The photoperiodic conditions under which the boar was kept were not specified. Accord ing to McConnell and Ellendorff [10], the plasma melatonin profile in domestic adult German Landrace sows is determined by the photoperiod environment to which the animals are exposed. Thus, under photoperiodic conditions of LD 12: 12 they found that 3 of 4 sows exhibited a nighttime rise in plasma melatonin (the increase ranged from 2 to 5-fold). However, when the animals were shifted to a summer photoperiod,

The effect of feed restriction and of a β-adrenergic agonist on plasma melatonin concentrations in domestic pigs

“…Paterson et al (L992a,b) (Reiter et al 1987) or circularing melatonin (Minton et al 1989) The lack of a nocturnal increase in melatonin secretion in pigs is apparently not due to a lack of the enzymes necessary for melatonin synthesis (Reiter et al 1987). Ir also appears from the present study that the pig pineal is capable of synthesizing melatonin in response to a p-adrenirgic fgonist.…”

“…Recently, Booth (1990) Reiter et al (1987) Therefore, although some reports indicate that the domestic pig appears to differ from other species in its secretion of melatonin, it seems that physiological systems are in place to allow both production and secretion of the hormone.…”

‘Synaptic’ Bodies in the Pineal Glands of the Cow, Sheep and Pig

“…In this context it is interesting that the concentration of melatonin is rather similar in porcine, ovine and bovine pineal glands during the morning hours [32]. In contrast to the cow and sheep, however, there is no nocturnal rise in melatonin in the pineal gland of castrated male and intact female pigs kept under natural photopcriodic and tem perature conditions [20]. In another study only very low elevations of plasma melatonin were detected in sexually immature female domestic pigs with nighttime levels much lower than those found in other species [33], Although there is apparently no typical day/night rhythm of melatonin synthesis in the porcine pineal gland [20], small numbers of SR were found in this study, whereas in the cow and sheep, in which melatonin production increases at night, no typical SR were detected.…”

“…In contrast to the cow and sheep, however, there is no nocturnal rise in melatonin in the pineal gland of castrated male and intact female pigs kept under natural photopcriodic and tem perature conditions [20]. In another study only very low elevations of plasma melatonin were detected in sexually immature female domestic pigs with nighttime levels much lower than those found in other species [33], Although there is apparently no typical day/night rhythm of melatonin synthesis in the porcine pineal gland [20], small numbers of SR were found in this study, whereas in the cow and sheep, in which melatonin production increases at night, no typical SR were detected. These arguments might further strengthen the hypothesis that SR arc involved in processes of intercellular communica tion rather than in the regulation of melatonin production [22.…”

Circadian variation of portal, arterial and venous blood levels of melatonin in pigs and its relationship to food intake and sleep

“…Surprisingly, in domestic pigs, the daily profile of melatonin has not been clearly established. No midnight increase of melatonin was observed in the pineal gland of pigs exposed either to a long or short photoperiod [Reiter et al, 1987]. In addition, no nocturnal increase of melatonin levels in serum was observed in a long [Minton et al, 1989] or short photoperiod [Brandt et al, 1986].…”