2. THE PINEAL ORGAN
101
(1959a) and the presence of a well-developed Golgi complex in the s u p
porting cells and the sensory cells ( Rudeberg, 1968b) indicate secretory
activity.
2. INTERNAL SECRETION
There is also the possibility of an internal secretory or endocrine role.
Although both Friedrich-Freksa (1932) and U. Holmgren (1959a) suggest that some pineal secretion is taken up by the blood vessels in teleosts, Hafeez and Ford (1967) did not find any secretory granules
within the nerve fibers or in the proximity of the blood vessels of sockeye salmon, Oncorh ynchus nerka. However, since the demonstration
of secretory granules depends upon the nature of the secretion and on
the specificity of the techniques employed, an internal secretory role
of the pineal organ was not definitely ruled out and few investigators
have applied techniques suitable for detecting the one known mammalian pineal hormone melatonin (Axelrod et aZ., 1960).
Melatonin (Fenwick, 1970a) and its precursor serotonin, (Fenwick,
1970a; Owman and Rudeberg, cited in Rudeberg, 196813) together with
the enzyme HIOMT (Quay, 1965) necessary for the formation of melatonin (Axelrod et al., 1!360), have now been demonstrated in fish pineal
organs. Also, Oguri et al. (1968) report that the pineal takes up more
14C-5-hydroxytryptophan than any other tissues studied. Since this
substance is a precursor of serotonin, an active tryptophan metabolism
within the fish pineal organ is indicated. Thus, an endocrine role of the
fish pineal, possibly based on the hormone melatonin, is not improbable.
Despite earlier reports by Krockert (1936a,b) that the growth rate
of young Lebistes could be decreased by feeding them desiccated bull
pineal glands, Pflugfelder (1953, 1954, 1956a) clearly implicated the
pineal as an endocrine organ of fishes and suggested a pineal-pituitary
relationship in teleosts. His observations on pinealectomized guppies
indicated hypertrophy of the adenohypophysis, hyperthyroidism, decreased growth rate, a slight acceleration in the appearance of secondary
sex characteristics in young males, an increase in the activity of the interrenal cells, and a disturbed calcium metabolism resulting in spinal
curvature. The thyroidal effects could be partially offset by the injection
of epiphysan or thyroxin (Pflugfelder, 1956b). Pflugfelder ( 1964) has
since reported alterations in the pars distalis and thyroid in pinealectomized goldfish. U. Holmgren (1959b) reported similar findings with
regard to skeletal abnormalities and was able to reduce these by administering beef pineal injections. Further, the latter investigator reported a
decreased radiocalcium uptake in pinealectomized fish and an increased
101
(1959a) and the presence of a well-developed Golgi complex in the s u p
porting cells and the sensory cells ( Rudeberg, 1968b) indicate secretory
activity.
2. INTERNAL SECRETION
There is also the possibility of an internal secretory or endocrine role.
Although both Friedrich-Freksa (1932) and U. Holmgren (1959a) suggest that some pineal secretion is taken up by the blood vessels in teleosts, Hafeez and Ford (1967) did not find any secretory granules
within the nerve fibers or in the proximity of the blood vessels of sockeye salmon, Oncorh ynchus nerka. However, since the demonstration
of secretory granules depends upon the nature of the secretion and on
the specificity of the techniques employed, an internal secretory role
of the pineal organ was not definitely ruled out and few investigators
have applied techniques suitable for detecting the one known mammalian pineal hormone melatonin (Axelrod et aZ., 1960).
Melatonin (Fenwick, 1970a) and its precursor serotonin, (Fenwick,
1970a; Owman and Rudeberg, cited in Rudeberg, 196813) together with
the enzyme HIOMT (Quay, 1965) necessary for the formation of melatonin (Axelrod et al., 1!360), have now been demonstrated in fish pineal
organs. Also, Oguri et al. (1968) report that the pineal takes up more
14C-5-hydroxytryptophan than any other tissues studied. Since this
substance is a precursor of serotonin, an active tryptophan metabolism
within the fish pineal organ is indicated. Thus, an endocrine role of the
fish pineal, possibly based on the hormone melatonin, is not improbable.
Despite earlier reports by Krockert (1936a,b) that the growth rate
of young Lebistes could be decreased by feeding them desiccated bull
pineal glands, Pflugfelder (1953, 1954, 1956a) clearly implicated the
pineal as an endocrine organ of fishes and suggested a pineal-pituitary
relationship in teleosts. His observations on pinealectomized guppies
indicated hypertrophy of the adenohypophysis, hyperthyroidism, decreased growth rate, a slight acceleration in the appearance of secondary
sex characteristics in young males, an increase in the activity of the interrenal cells, and a disturbed calcium metabolism resulting in spinal
curvature. The thyroidal effects could be partially offset by the injection
of epiphysan or thyroxin (Pflugfelder, 1956b). Pflugfelder ( 1964) has
since reported alterations in the pars distalis and thyroid in pinealectomized goldfish. U. Holmgren (1959b) reported similar findings with
regard to skeletal abnormalities and was able to reduce these by administering beef pineal injections. Further, the latter investigator reported a
decreased radiocalcium uptake in pinealectomized fish and an increased