Reprinted from Science, July 19, 1963, Vol. 141, No. 3577, pages 277-278
Copyright O 1963 by the American Association for the Advancement of Science
of melatonin daily for 10 days, the normal diurnal variation. When estrous
increments in thyroid-cell height and rats, exposed to constant light, were
I''l uptake produced by methylthioura- given melatonin (10 ug subcutaneously), the incidence of estrus was reAbstract. Daily injection of micro- cil were diminished (8).
duced to 45 percent, while animals
gram amounts of rielatonin in rats degiven diluent alone showed no change.
creased the incidence of estrus and
2. Effect of melatonin on the estrous cycle This effect was observed for only the
reduced ovarian weight. Circulating Table
of the rat. Animals received 0.2 ml of diluent
melatonin was selectively taken up and or 20 jg of melatonin, intraperitoneally. Vaginal first day after injection; subsequently,
retained by the ovary and pineal gland; smears were taken daily after vaginal opening animals that received melatonin re14 to 19 smears were taken from each ani- turned to a normal estrous cycle. It
this effect was reduced by exposure of and
mal. Results are expressed as the percentage of
rats to constant light. A single injection the total number of smears indicating estrus was not possible to inhibit the onset
were taken from each animal. The inci- of light-induced persistent estrus by
of melatonin lowered the incidence of which
dence of estrus in rats receiving melatonin means of daily injections of 10 ag of
to
constant
estrus among rats exposed
differed significantly (p < .01) from that of
melatonin.
animals receiving placebo.
light.
Thus, melatonin appears to satisfy
Smears
Rats (No.)
ndcSmears
classical criteria for a hormone. (i)
the
indicating
Many observations have linked the
Control
Melatonir
estrus
produced by a specialized glanduIt
is
funcmammalian pineal gland to gonad
,ar structure: only the pineal gland has
tion. Human males with tumors which
3
0
0-20
the enzyme required for its synthesis
destroy the pineal gland have a high
5
2
21-40
(7, 10). (ii) It is released into the
incidence of' precocious puberty (1).
3
7
41-60
circulation: melatonin is endogenously
Pinealectomy has resulted in an increase
0
2
61-80
present in peripheral nerve, a tissue
in ovarian weight (2), while pineal ex0
0
81-100
which does not make it but can take
tracts decreased ovarian weight and
it up from the circulation. (iii) It has
the
rat
ovary.
melatonin
on
The
effect
of
Table 1.
Our experiments show that some of
an effect on a distant target organ: it
The diluent was 0.48 percent KCI and 0.18
percent NaCI. S., serotonin; M, melatonin; the effects of the pineal gland on gonad
alters such gross factors as ovarian
i.p., intraperitoneally; s.c., subcutaneously.
function might be mediated by melaweight and the estrous cycle. (iv) It
tonin. Immature female rats were given
Ovary weight - S.E.
Dose
Treatis not synthesized by the target organ;
(mg)
(mg) Route
ment
placebo, 50 ftg of serotonin, or 1 to 20
and'hydroxyindole-O-methyl transferase
/g of melatonin, intraperitoneally or
Groups of II rats (85 to 95 g)
could not be detected in rat or human
67.3 - 3.6
Control
subcutaneously, daily for 28 days. In
ovary. (v) It is taken up by the target
4.4
71.4
i.p.
50
S*
rats receiving melatonin, there was a
0.001)
(p
<
3.2
42.6
i.p.
20
M
organ from the circulation. Melatonin
delay in spontaneous vaginal opening,
Groups of 10 rats (45 to 55 g)
is taken up by the brain, and concenand a highly significant decrease in
49.0 - 2.8
Control
trated by the pituitary and ovary; thus,
2.6
46.0
i.p.
I
M
ovarian weight (Table 1) and in the
its effects on ovarian weight and func0.05)
(p
<
2.0
41.3
i.p.
10
M
incidence of vaginal estrus (Table 2). tion could result from an action at any
39.1 - 2.9 (p < 0.05)
s.c.
I
M
As little as I pkg of melatonin, admin- of these sites.
*As serotonin creatinine sulfate.
istered subcutaneously, caused a sigThere is considerable evidence to
nificant decrease in the weight of the
show that the state of the pineal is
produced anestrus in aged rats with ovary. Larger doses of serotonin, the related to environmental changes. Varispontaneous persistent estrus (3). When precursor of melatonin, produced none ations in day length produced changes
rats were exposed to constant light the of the vaginal and ovarian effects but in pineal cytology and serotonin content
ovaries became enlarged and the in- caused a significant increase in adrenal (11); exposure to constant light altered
cidence of estrus increased; both effects weight. Neither compound altered body pineal size, cellular morphology, and
are inhibited by the administration of or uterine weight.
chemical content. It is possible that the
Tritiated melatonin (9); when ad- physiological disposition and actions of
pineal extracts (4). Exposure to light
produced a decrease in pineal weight, ministered to four cats intravenously, melatonin might be influenced by light
serotonin content, and nucleolar size was selectively taken up in endocrine (12).
(5). Thus, some of the effects of light and peripheral nervous tissues, espeRICHARD J. WURTMAN
on the gonads may be mediated by the cially in the ovary and the pineal gland.
JULIUS AXELROD
One hour after administration, the conpineal gland.
ELIZABETH W. CHU
Melatonin (5-methoxy-N-acetyltryp- centration of H-meiatonin in the ovary Laboratory of Clinical Science,
tamine) is highly localized in the mam- was 5 to 25 times that in the peripheral National Institute of Mental Health,
malian pineal gland (6), and small tissues, 2 to 3 times that in the thyroid, and Department of PathologicAnatomy,
amounts also occur in peripheral pituitary, and adrenal glands and the Clinical Center, National Institutes
nerves (6). An enzyme, hydroxyindole- peripheral nerves, and one-third that in of Health, Bethesda, Maryland
O-methyl transferase, required for the the pineal gland.
References and Notes
When 100 rats were kept in constant
synthesis of melatonin is present exthen
4
weeks
and
light
for
or
normal
1. J. I. Kitay, J. Clin. Endocrinol. Metab. 14,
clusively in the pineal gland (7). Very
622 (1954).
small amounts of melatonin produce a given H3-melatonin intravenously, the
2. Y. Izawa, Trans. Japan. Pathol. Soc. 16, 72
(1926); H. Simonnet, L. Thidblot, T. Melik,
lightening effect on amphibian mela- uptake by the pineal gland and ovary
Ann. Endocrinol. 12, 202 (1951); J. I. Kitay,
nocytes (6), but melatonin has not been was significantly reduced. Vaginal
Endocrinology 54, 114 (1954).
3. R. J. Wurtman, M. D. Altschule. U. Holmstudied in that class. Recently, Ba- smears of these animals showed an 85
gren, Am. J. Physiol. 197, 108 (1959); C. J.
schieri et al. have reported that when percent incidence of estrus, as compared
Meyer, R. J. Wurtman. M. D. Altschule, E. A.
Lazo-Wasem, Endocrinology 68, 795 (1961).
rats were given large doses (150 jug) with 50 percent in animals exposed to
Melatonin, a Pineal Substance:
Effect on the Rat Ovary
1
4, V. M, Fke. Ihlil. 29. 17 (1941): W. Jochle.
Eil¢okrinioluglth 33. 2X7 (1956: J.
. IlTt.
Endocrinolot,
71. 1l (1962): R. J.
'turtman. W, Roth. M. D. Altsehule. J. J. Wurtm:an, Alet Erlrol. 36, 617 (1961).
5. V. M Fiske. J. Pound. J. Putnam. Eldtocrldtology71. 130) (1962); W B..t Q'y nd A.
Halcvy, Phytlol. Zol. 35, I (1962): W. ).
Roth, R. J Wulrtmuan, h
D. Altschule.
F'ntocrlnlovey 71. 88 (1962).
6. A. B. Lrner. J. 1). Cse. R. V. Heinzelmn,
J. Am ( lhentm.
Sc. 81. 60(84 (1959).
7, J. Alrod. P. D), MacLean. R. W. Albers. H.
Weissb:ch. ill Regiool .iNetirochepmlstry. S. S.
K;e'y
nd J. Elkes. Eds. (Pergamon,. Nw
York,. 19611. p)p, 3107-31 1.
8, I.. I;nschricrl F. )l.uca.
.. Cramarossa. C.
I)eNlarlin
A. Oliverlo, N1. Ncgri.
xperlentit) 19. 1 (1963).),
9. .Mc Ilnonin-aclityl-t
prepared by thie method
of I. J. Kopin. C, . B. Pare, J. Axelrod. H.
\VWisslanch. J. lot, ('lhem. 236, 3(172 (1961).
10, HydroxyIndolc-O-methyl transferase wvauexamined n 11 human pineal glandm obtained at
;lutopsy by the method of Axelrod landWeissbach J. Blol. Chem. 236. 211 (1961)]. The
enzyme uctlivlty wans suillicint to synthesize
2411 ' 31ql of melatonin per gram of tissue
per hour. Calcified glands from aged suhjects
have a s muIch enzyme activity as uncalclfied
Ia ndi.
11. W, B,. Quay. J. Morphol. 98, 471 (1956);
perlsonal com nmunicalion.
12, We thalnk L. Strloud for technical asslstancc.
2 April 1963
Reprinted with permission by the
U. S. DEPARTMENT OF HEALTH, DUCATION, AND WLFARE
Public Health Service
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