Twenty-Four-Hour Cycle of a Melatonin-Like Substance in the Plasma of Human Males

Pelham, Russell W.; Vaughan, George M.; Sandock, Kenneth L.; Vaughan, Mary K.

doi:10.1210/jcem-37-2-341

Cited by 114 publications

(38 citation statements)

References 9 publications

(10 reference statements)

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“…This phenomenon may be due to increased pineal synthesis and secretion of melatonin following blinding. Blinding or constant darkness results in a large increase in the activity of the melatonin-synthesizing enzymes in the rat pineal (28,29), and recently it was shown (30) that the concentration of a melatonin-like substance increases in the plasma of humans kept in darkness.…”

Section: Discussionmentioning

confidence: 99%

Suppression of Human Growth Hormone Secretion by Melatonin and Cyproheptadine

Smythe¹,

Lazarus²

1974

J. Clin. Invest.

138

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A B S T R A C T Pituitary growth hormone (GH) release in the rat is stimulated via serotoninergic pathways and can be inhibited by treatment with compounds that act as serotonin antagonists, such as cyproheptadine or the pineal gland hormone, melatonin. To investigate a possible role for serotonin in the control of human GH release, the effects of cyproheptadine and melatonin administration on the GH responses of normal. male subjects were examined.The oral administration of cyproheptadine (8-12 mg daily for 5 days) to normal subjects reduced their GH responses to both insulin-induced hypoglycemia and physical exercise to a highly significant extent. Similarly, the mean GH responses of 10 subjects to insulin-induced hypoglycemia were significantly reduced after the prior oral administration of melatonin (1 g).The data presented show that serotonin antagonism has a similar effect on GH secretion in man to that observed in the rat and provides further evidence for serotoninergic, and possibly pineal, involvement in the control of human GH secretion.

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Section: Discussionmentioning

confidence: 99%

Suppression of Human Growth Hormone Secretion by Melatonin and Cyproheptadine

Smythe¹,

Lazarus²

1974

J. Clin. Invest.

138

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“…The serum serotonin of the rat increases at the beginning of the dark phase, but also at the end of the light phase Ralph, 1975). Melatonin secretion has also been observed to increase at the beginning of darkness in ewes (Rollag and Niswender, 1976) and in man (Pelham et al,1973 …”

mentioning

confidence: 96%

“…In the rat, pinealectomy abolishes the diurnal rhythm in prolactin secretion (Ronnekleiv et al, 1973) as well as blocking the increase in prolactin observed in rats kept in continuous darkness (Relkin, 1972) Ralph, 1975). Melatonin secretion has also been observed to increase at the beginning of darkness in ewes (Rollag and Niswender, 1976) and in man (Pelham et al,1973 Acknowledgments. …”

mentioning

confidence: 98%

Light control of prolactin secretion in sheep. Evidence for a photoinducible phase during a diurnal rhythm

Ravault¹,

Ortavant²

1977

Ann. Biol. anim. Bioch. Biophys.

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Summary. The secretion of prolactin comes under important seasonal variations in sheep. Thus, in the ram the highest levels are in summer and the lowest in winter. These variations of secretion are under light control because illumination of long duration (long photoperiods) produces high prolactin levels (220 -L 2 ng) ; short photoperiods produce low levels (12 ! 2 ng).Using the hypothesis of Bunning, we study a photoinducible phase during diurnal rhythm. For this purpose, rams preconditioned either in short photoperiods or in long photoperiods, receive 8 hours of illumination in two fractions of 7 and 1-hour durations. The beginning of the 7-hour period is considered to be a subjective dawn, and the 1-hour light pulse is given at various times after dawn : at hours 11, 14, 17 and 20.The group receiving the light pulse during hour 17 after dawn has significantly higher prolactin levels than all the other groups. For example, in rams preconditioned in short photoperiods and after 5 weeks of light pulse treatment, the mean prolactin levels are 71 ! 4 ng (hour 11)) ; 68 ! 5 ng (hour 14) ; 225 ! 22 ng (hour 17) and 110 ! 16 ng (hour 20). The (Pelletier, 1973) (Tucker et al., 1973 ;Schams and Reinhardt, 1974) and in goats (Buttle, 1974 ;Hart, 1975). One of us (Ravault, 1976) (Kann, 1971) (Hamner, 1963(Hamner, , 1964Farner, 1965 ;Menaker, 1965 ;Follett and Sharp, 1969 ;Follett, 1973 ;Lofts and Lam, 1973 Ronnekleiv, Krulich and MacCann, 1973 ;Simionescu, Sahleanu and Oprescu, 1974 ;Kizer et al., 1975), in the pregnant rat (Butcher, Fugo and Collins, 1972) or in the pseudopregnant rat (Freeman and Neill, 1972), in the ewe during the luteal phase (Davis and Borger, 1972), in the lactating cow Convey, 1970, 1972), in the rhesus monkey (Quadri and Spies, 1976) and in man (Sassin et al., 1972 ;Vanhaelst et al., 1973 ; Rubin et at., 1975 (Buttle, 1974).We have studied the evolution of plasmatic prolactin level during the diurnal cycle in rams before the beginning of light pulse treatment, using either long photoperiods (June 8) or short photoperiods (December 15), and then on the same rams about five weeks after the beginning of the light pulse treatments.In all groups, the mean prolactin level was higher in the dark than in the light phase. For example, in the pretreatment period ( fig. 6), the mean prolactin level in 30 rams was 190 ! 9 ng/ml (long photoperiods) and 32 ! 4 ng/ml (short photoperiods) during the dark, compared with 112 ! 5 ng/ml and 6 ± 1 ng/ml during the light phases. The results after about one month of light treatment are shown in table 2.This difference is due to the sharp increase in prolactin in the hour after the change from light to dark ( fig. 7, 8). A high level is subsequently maintained for 2-3 hours, then falls gradually. The short duration of this peak explains why several authors have not found diurnal variations : blood sampling was not frequent enough.Other low but significant peaks of prolactin were observed either at the end of the dark phase on rams preconditioned to short p...

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“…Fluctuations in blood melatonin levels in response to a light-dark transition have been demonstrated in the sheep (Rollag and Niswender 1976), the rat (Ozaki et al 1976) and in man (Pelham et al 1973). The present work has established that in M. leonina blood melatonin levels exhibit a circadian variation, which is much more marked in winter (approximately 16 h of darkness) than in summer (approximately 5 h of darkness).…”

Section: Discussionmentioning

confidence: 99%

Summer and Winter Cycles in Plasma Melatonin Levels in the Elephant Seal (Mirounga Leonina)

Griffiths¹,

Seamark²,

Bryden³

1979

Aust. Jnl. Of Bio. Sci.

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Plasma melatonin concentration of immature male elephant seals was determined by radioimmunoassay. Comparison of concentrations during two 24-h periods, one in midsummer and one in midwinter, showed that there was a marked circadian cycle in winter which was greatly modified during the long day length of summer. It is suggested that in summer there was sufficient ambient lighting during the night hours to depress the nocturnal rise in plasma melatonin. The complexity of pineal cycles in the natural environment is stressed, and in this regard the polar regions are of particular interest due to the extreme seasonal changes in day length there.

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Twenty-Four-Hour Cycle of a Melatonin-Like Substance in the Plasma of Human Males

Cited by 114 publications

References 9 publications

Suppression of Human Growth Hormone Secretion by Melatonin and Cyproheptadine

Suppression of Human Growth Hormone Secretion by Melatonin and Cyproheptadine

Light control of prolactin secretion in sheep. Evidence for a photoinducible phase during a diurnal rhythm

Summer and Winter Cycles in Plasma Melatonin Levels in the Elephant Seal (Mirounga Leonina)

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