Stannius corpuscles and plasma calcium levels during the reproductive cycle in the cichlid teleost fish, Oreochromis mossambicus

Abstract

The corpuscles of Stannius (CS) of the cichlid Oreochromis mossambicus (formerly Sarotherodon mossambicus) were studied in relation to sexual maturation and plasma calcium levels. After sexual maturation, the CS are enlarged in female fish, because of an increase in size and number of the type-1 cells. During the ovarian cycle, the size of the CS increases in parallel with the growth of the ovaries. Concurrently, plasma total calcium increases markedly until spawning. This increase is mainly accounted for by calcium bound to proteins (vitellogenins), but the ultrafiltrable calcium fraction is also slightly higher than in males. Ovariectomy is followed by a reduction in the size of the CS, mainly a result of involution of the type-1 cells, and by a reduction in plasma calcium to levels typical for males. Gonadectomy in males does not affect size or ultrastructure of the CS, or plasma calcium levels. Since the type-1 cells of the CS are the presumptive source of a hypocalcemic hormone, we conclude that activation of the CS during the female reproductive cycle is a response to elevated calcium levels that accompany ovarian maturation. We suggest that the CS respond in particular to the elevated ultrafiltrable or ionic calcium levels.

Immunocytochemical localization of hypocalcin in the endocrine cells of the corpuscles of Stannius in three teleost species (trout, flounder and goldfish)

“…Similar cells have been described in, e.g., trout (Meats et al 1978), coho salmon Fig. 7; preabsorption control, x 45000 (Aida et al 1980), tilapia (Urasa and Wendelaar Bonga 1985), and the holostean Lepisosteusplcityrhynchus (Bhattacharya et al 1982). In almost all of these species, the type-1 and type-2 cells show similar marked differences in cellshape, granule-size and extent of the granular endoplasmic reticulum.…”

“…From this divergence, it seems plausible to conclude that the two cell-types have different functions and produce different hormones. Type-1 cells are thought to produce the hypocalcemic principle (Wendelaar Bonga et al 1980;Urasa and Wendelaar Bonga 1985;Kaneko et al 1988). They become activated upon transfer of euryhaline fish from fresh water to seawa ter (Cohen et al 1975;Wendelaar Bonga et al 1976;Meats et al 1978).…”

“…This activation is related to the change in ambi ent Ca2~ (Wendelaar Bonga et al 1976;Meats et al 1978), as it does not occur when fish are transferred from fresh water to calcium-deficient seawater (Cohen et al 1975;Wendelaar Bonga et al 1980). This cell-type is also activated in high-calcium fresh water or during ovarian maturation, conditions associated with hypercalcemia (Ur asa and Wendelaar Bonga 1985Bonga , 1987. Conversely, type-2 cells are not affected by changes in the calcium content of the ambient water (Wendelaar Bonga et al 1976Meats et al 1978), and their activity is reduced by fresh water to seawater transfer (Meats et al 1978;Wendelaar Bonga et al 1976;.…”

Prospect of a stanniocalcin endocrine/paracrine system in mammals

“…The NH 2 -terminal half of STC2 is cysteine rich, suggesting that STC2 may also form dimers, as is the case with STC1 and fish STC. Indeed, native hamster STC2 has been shown to form a disulfide-linked homodimer with a subunit size of [35][36][37][38][39][40]. The sites of a con- ϩ RNA from various rat tissues (Clontech) were hybridized with 32 P-labeled rat STC1 cDNA.…”

“…Therefore, STC is an important regulator of Ca in both marine and freshwater fish. Interestingly, roles of STC other than Ca homeostasis are reported: phosphate homeostasis (25) and ovarian function (39). Presently, active research on fish STC continues because its receptor and signaling mechanisms have not yet been clarified.…”