ISSN:
1432-136X
Keywords:
Prolactin
;
Growth hormone
;
Calcium
;
Pituitary
;
Eel, Anguilla japonica
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract Effects of changes in environmental Ca2+ on the secretion of prolactin, a possible hypercalcemic hormone, were examined both in vivo and in vitro in the Japanese ecl, Anguilla japonica. Transfer of seawater- or freshwater-adapted fish to fresh water, fresh water containing 10 mmol Ca2+ · 1-1 sea water, Ca2+-free sea water, or deionized water was accompanied by significant changes in plasma Ca2+ levels after 7 days, except for the fish transferred from fresh water to fresh water and from sea water to sea water. Changes in external Ca2+ concentrations did not affect plasma prolactin levels, although plasma prolactin levels as well as pituitary prolactin contents were significantly greater in fish in a hypotonic environment than those in a hypertonic environment, regardless of the external Ca2+ concentration. Hypercalcemia, induced by removal of the corpuscles of Stannius, did not alter plasma prolactin levles. Incubation of the pituitary in the medium with different Ca2+ concentrations (up to 2.9 mmol·l-1) did not affect the basal release of prolactin, except at an extremely low Ca2+ concentration (less than 0.1 mmol·l-1) where prolactin release was inhibited. Addition of Ca2+ ionophore (A23187) to the medium led to a marked and significant increase in prolactin release, indicating that an increase in intracellular Ca2+ stimulates prolactin release. However, the effect was not specific to prolactin cells; a similar increase was seen in growth hormone release. These results indicate that changes in environmental Ca2+ concentration may not be the primary factor influencing prolactin secretion in the eel; changes in environmental osmolality or Na+ levels seem to be more critical for the regulation of prolactin secretion.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00263593
