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

Plasma immunoreactive melatonin was monitored for 110 hr in sexually immature female domestic pigs kept under 12L:12D light conditions and treated with two sympathicolytic (alpha-methyl-p-tyrosine, propranolol) and three sympathicomimetic (clorgyline, isoproterenol, dobutamine) drugs. Mean levels of plasma melatonin in the control pigs showed significant diurnal changes with the highest values during the scotophase. In the individual gilts the diurnal changes of plasma melatonin were markedly irregular; melatonin increases were not consistently noted at night, and melatonin levels during light and darkness varied considerably between days. The lack of consistency in the diurnal patterns of plasma melatonin in individual pigs during consecutive days explains the large inter-individual differences observed in previous short-term studies. Administration of alpha-methyl-p-tyrosine resulted in the decrease in both daytime and nighttime melatonin levels, compared with the control group, but it did not eliminate the increases in melatonin during the night. Treatment with other drugs did not significantly change the level of plasma melatonin compared with the control group, however they had modulatory effects on melatonin rhythm. The results suggest that the plasma melatonin in the domestic pig is controlled by the adrenergic nervous system, but the pharmacology of the secretion and/or metabolism of this pineal hormone is different than described in other species.

Section: Discussionmentioning

confidence: 96%

Effects of sympathicolytic and sympathomimetic drugs on plasma immunoreactive melatonin in the domestic pig

Lewczuk

Przybylska‐Gornowicz

1997

“…However, even in studies where a nocturnal peak was observed, not all pigs exhibited elevated levels during the scotophase. Therefore, Peacock et al [1995] concluded that “at least some pigs fail, under circumstances that remain unclear, to secrete melatonin”. Our present study may provide another explanation for the inconsistency in circadian variation of melatonin in pigs.…”

Section: Discussionmentioning

confidence: 99%

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

Bubenik¹,

Pang²,

Cockshut³

et al. 2000

Circadian levels of melatonin were determined in the hepatic portal vein, cranial vena cava, and the lower aorta of ten juvenile pigs. Blood was sampled every hour for a total of 24 hr via temporary cannulas introduced into blood vessels under anesthesia. No peak levels of melatonin were found in the mid-scotophase, but hepatic portal concentrations peaked at 06.00 hr. Overall levels of melatonin were highest in the hepatic portal vein (range 35-65 pg/mL), followed by an artery (range 30-55 pg/mL) and the vena cava (range 25-35 pg/mL). Levels of melatonin exhibit strong variation between individual pigs, but generally the average levels from all three sources follow each other's time course. However, on occasion, melatonin levels in the hepatic portal vein varied independently from the levels in the vena cava. Large portal peaks were usually preceded by a feeding period and were associated with a subsequent period of sleep. The data indicate that: 1) there is no clear circadian rhythm of melatonin in the peripheral blood of pigs, 2) relatively little melatonin is metabolized during the first liver passage, 3) food intake may elevate melatonin levels in the hepatic portal vein, and 4) increased levels of melatonin originated in the gastrointestinal tract may induce sleep.

“…None of these are a suitable model for studies of human digestive processes. The pig, a large monogastric, omnivorous animal, was recently introduced, as a model for studies of interaction between melatonin and the GIT [Peacock et al, 1995;Ayles et al, 1996;Bubenik et al, 19961. In order to investigate the previously described protective effect of melatonin on the incidence of GU, two studies were performed. In the first one, ulcer scores and levels of melatonin in plasma and GIT tissues were determined after 4 weeks of dietary supple-mental unit.…”

Section: Introductionmentioning

confidence: 99%

Relationship between melatonin levels in plasma and gastrointestinal tissues and the incidence and severity of gastric ulcers in pigs

Bubenik¹,

Ayles²,

Friendship

et al. 1998

Four weeks of administration of melatonin mixed in the diet (5 mg/kg of food) significantly reduced the incidence of gastric ulcers in young pigs. In control and melatonin supplemented animals, significantly higher levels of melatonin were found in the stomach tissues as compared to jejunum, ileum, or colon. Pigs with the most severe ulcers exhibited significantly lower concentrations of melatonin in their stomach tissue and the blood plasma. Pigs fed coarsely ground diet exhibited higher tissue levels of melatonin in the stomach than animals fed a finely ground diet. Coarse diet was also associated with a lower score of gastric ulcers. No relationship between tissue levels of melatonin and the severity of gastric ulcers was found in other segments of the gastrointestinal tract. In the second experiment we determined that there was no significant difference between the gastro-protective effects of 2.5, 5.0, and 10.0 mg of melatonin mixed per 1 kg of food. A coarsely ground diet is hypothesized to have a gastro-protective effect by stimulating the production of melatonin in the stomach tissues. Dietary supplementation of food with melatonin, at threshold levels perhaps lower than 2.5 mg/kg/feed, may significantly reduce the incidence of gastric ulcers in pigs.