IUBio Biosequences .. Software .. Molbio soft .. Network News .. FTP

Melatonin and Growth Hormone

Dag Stenberg stenberg at cc.Helsinki.FI
Tue Jan 16 12:26:18 EST 1996


Dan Komaromi (komaromi at ucla.edu) wrote:
} In my brief introduction to melatonin, I've heard reports that it
} stimulates growth hormone.  Would this allow for any growth after an
} organism's normal growth period, or simply increase the growth rate
} during this period?
}

I am not familiar with the relationship between MEL and GH, but 
according to the literature MEL seems to increase GH secretion by 
indirect, possibly hypothalamic mechanisms in adult subjects. The
situation is different in immature subjects.

* Exogenous MEL (2 mg orally) did not change the GH secretion of healthy
volunteers (Wright &al, Clin.Endocrinol. 24:375-382, 1986).
#* 0.5 mg MEL orally was found to increase plasma GH levels of healthy 
male volunteers, and also to increase the plasma GH response to GHRH
(Valcavi &al, Clin.Endocrinol. 26:453-458, 1987).
* 80 or 240 mg (!) MEL orally to healthy males had a slight, statistically
nonsignificant increasing effect on GH, while for instance strongly
increasing prolactin secretion (Waldhauser &al, Neuroendocrinology
46:125-130, 1987).
* Plasma GH (and prolactin) was measured from normal men during sleep
deprivation, combined with either bright light (which inhibits MEL), dim
light, or bright light + exogenous MEL infusion. In this model, MEL had
no effect on the changes induced by sleep deprivation (Strassman &al,
J.Clin.Endocrin.Med. 65:847-852, 1987.
#* 0.4 mg/kg MEL was injected to healthy subjects at 09:00 a.m., and 
a significant increase was found in plasma GH. The rise could be blocked
by naloxone, indicating that the effect of MEL might be mediated 
by opioids (Esposti &al, J.Endocrinol.Invest. 11:103-106, 1988).
#* 10 mg MEL orally in the afternoon had a weak stimulatory effect 
on basal GH secretion in normal males, but doubled the increase in GH
induced by GHRH (Valcavi &al, Clin.Endocrinol. 39:193-199, 1993). This
indicates that MEL may inhibit somatostatin, the hormone normally
antagonizing the stimulatory effect of GHRH on GH.
#* 0.5 to 2 mg MEL orally increased GH secretion in a patient who lacked
endogenous MEL (Petterborg &al., Brain Res.Bull. 27:181-185, 1991).

There are thus several studies (#*) indicating that MEL increases GH 
secretion in humans. Some studies also indicate that this is the case 
in animals:

#* Daily injections of MEL in the evening increased GH secretion in
Syrian hamsters (Vriend &al., Growth, DEvel. and Aging 54:165-171, 1990).
#* MEL had no effect on basal secretion of GH in Syrian hamsters, 
but prevented thyroxine from reducing GH levels to normal in
experimentally hypothyroid hamsters (Vriend &al, Growth 51:35-43, 1987).
* Subcutaneously implanted MEL pellets increased plasma GH
significantly in pigeons, but this was attributed to a change in
metabolism because the normal day-night fluctuation in MEL was, of
course, eliminated (John &al., Gen. & Comp.Endocrinol. 79:226-232,
1990).

The effect of MEL must be indirect and not direct on the pituitary
GH-producing cells:
* MEL mildly inhibited GH production in rat pituitary gland culture
(Griffiths &al. Acta Physiol.Scand. 131:43-49, 1987). 
* MEL had no effect on GH secretion of mink pituitary gland cultures
(Meunier &al., J.Endocrinol. 119:287-292, 1988).
* MEL had no effect on GH production or GH responses to GHRH in rat
pituitary culture (Valcavi &al., Clin.Endocrinol. 26:453-458, 1987).


MEL may inhibit GH secretion in immature organisms:
* MEL decreased GH in healthy prepubertal subjects, but had no effect in
8 of 10 pubertal subjects, while it increased GH in 2 of the 10 pubertal
subjects (Lisoni &al., Acta Endocrinol. 111:305-311, 1986).
* Plasma MEL and GH were negatively correlated in children (Gupta, 
J.Neur.Transm. Suppl. 21:217-232, 1986).
* and last, there is a Russian paper indicating MEL-mediated inhibition 
of rat pituitary GH cells in neonatal but not adult rats (Galstian &al.,
Problemy Endokrinologii 40:57-60, 1994).

As to the question:
Dan Komaromi (komaromi at ucla.edu) wrote:
} In my brief introduction to melatonin, I've heard reports that it
} stimulates growth hormone.  Would this allow for any growth after an
} organism's normal growth period, or simply increase the growth rate
} during this period?

it is clearly not possible to start speculating on the basis of
hitherto published data.

Dag Stenberg

------------------------------------------------------------------
Dag Stenberg     MD PhD                    stenberg at cc.helsinki.fi
Institute of Biomedicine		   tel: int.+358-0-1918532
Department of Physiology                   fax: int.+358-0-1918681
P.O.Box 9       (Siltavuorenpenger 20 J)   tlx: 1002125 finuh sf
FIN-00014 University of Helsinki,Finland   
        X.400:   /C=FI/A=FUMAIL/P=INET/O=HELSINKI/OU=CC/S=STENBERG/
------------------------------------------------------------------





More information about the Neur-sci mailing list

Send comments to us at biosci-help [At] net.bio.net