Pituitary cell types have been studied by application of specific histochemical methods. Identification of cell types in the fishes Anguilla anguilla, Pleuronectes platessa and Limanda limanda at different seasons and maturity stages is based on both tinctorial and structural characteristics of different cell types; their granulation, state of vacuolation, condition of the nucleus and presence or absence of the nucleolus. Gonads from fish caught monthly were also prepared for histological examination to determine their maturity stage and sex. Female A. anguilla at maturity stages II and III, and yellow in all external morphological characters, were used. A general cytohistological study of the pituitary gland during the annual cycle has been carried out with the aim of discovering (a) the causes of the longterm growth, and (b) the pituitary's physiological control of the fishes' metamorphosis. Variations in number and activity of the cell types to be found in the meso adenohypophysis have been investigated by cell counts of representative medial sagittal sections of the pituitary during different months. somatotrophs show short-term fluctuations, but gonadotrophs show an alternating cycle of increase and decrease. Chromophobes do not show much change in their number during the annual life-cycle. Basophils are found in all 3 lobes of the adenohypophysis and exhibit very little structural difference, so that a common function for all 3 cell types may be assumed. Observations on variations in concentration of neurosecretory material have been made; peak accumulation of neuroscretory material occurs between August and October and then remains almost constant up to December. This periodic increase suggests that neurosecretory substances have an influence upon the animal's metabolic activities. Studies in relation to the maturation cycle carried out on monthly samples of male and female P. platessa and L. limanda regarding the percentage, relative numbers and state of activity of chromophobes, somatotrophs and gonadotrophs produced results which appear to agree with the functions suggested for each cell group; their variation in number and activity keeps pace with corresponding maturity phases. Somatotrophs predominate in all maturity stages in both sexes. Chromophobes exhibit a cyclic increase and decrease; few are present in ripening gonads, many in spawning individuals. Gonadotrophs show a relative increase in number during gonadal ripening. Active and inactive gonadotrophs are identifiable at all maturity stages. The eel pituitary size is independent of both length and weight; however, for P. platessa pituitary size is related to weight, which is (in part) dependent upon the maturity stage. Implications of variations in relative proportions of cell types are discussed with regard to present knowledge of the pituitary gland.
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Jan 1, 1989
Sueo Enomoto + 1
Open Access
