Response of renal calcium-binding protein independence of kidney vitamin D hydroxylation

Dietary calcium and dietary phosphorus restriction were studied in chicks fed either cholecalciferol or 1α-hydroxycholecalciferol. Intestinal calcium absorption and calcium-binding protein of 1α-hydroxycholecalciferol-treated chicks remained unchanged under dietary calcium restriction, but increased under dietary phosphorus restriction. Kidney calcium-binding protein was not altered by dietary calcium restriction in chicks treated with either cholecalciferol or 1α-hydroxycholecalciferol, but increased under dietary phosphorus restriction independent of the vitamin D source. In contrast to the intestine, calcium-binding activity of the kidney was found to be poorly related to the calcium-binding protein concentration. It is suggested that kidney calcium-binding protein is regulated by a mechanism different from that of intestinal calcium-binding protein, and that its concentration in renal tissue is related to renal calcium excretion or plasma calcium level.     

Response of renal calcium-binding protein. Independence of kidney vitamin D hydroxylation.

Dietary calcium and dietary phosphorus restriction were studied in chicks fed either cholecalciferol or 1alpha-hydroxycholecalciferol. Intestinal calcium absorption and calcium-binding protein of 1alpha-hydroxycholecalciferol-treated chicks remained unchanged under dietary calcium restriction, but increased under dietary phosphorus restriction. Kidney calcium-binding protein was not altered by dietary caclium restriction in chidks treated with either cholecalciferol or 1alpha-hydroxycholecalciferol, but increased under dietary phosphorus restriction independent of the vitamin D source. In contrast to the intestine, calcium-binding activity of the kidney was found to be poorly related to the calcium-binding protein concentration. It is suggested that kidney calcium-binding protein is regulated by a mechanism different from that of intestinal calcium-binding protein, and that its concentration in renal tissue is related to renal caclium excretion or plasma calcium level.     

Characteristics of the rat liver microsomal enzyme system converting cholecalciferol into 25-hydroxycholecalciferol. Evidence for the participation of cytochrome p-450.

Properties of the rat hepatic cholecalciferol 25-hydroxylase have been studied. An assay system has been developed in which 25-hydroxycholecalciferol production is linear for at least 2h in both homogenates and microsomal fraction. Furthermore, the initial reaction velocity is linearly related to the amount of liver tissue or microsomal fraction. This enzyme system also metabolizes an analogue of cholecalciferol, namely dihydrotachysterol 3, into 25-hydroxydihydrotachysterol 3. The 25-hydroxylase is in the microsomal fraction and not in mitochondria. It has a Km of 44 nM for cholecalciferol and 360 nM for dihydrotachysterol 3. Its activity is not altered by dietary concentrations of calcium and phosphorus. Vitamin D-deficient rats have higher activities of the hepatic 25-hydroxylase than those receiving 25 ng of cholecalciferol daily. The 25-hydroxylase is inhibited by metyrapone. An atmosphere of CO/O2 (9:1, v/v) inhibits the reaction by 87%. This inhibition is partially reversed by white light. Additionally, cholecalciferol and 25-hydroxycholecalciferol competitively inhibit aminopyrine demethylase. These results support the idea that the cholecalciferol 25-hydroxylase is a cytochrome P-450-dependent mono-oxygenase.     

Maternal-perinatal interrelationships of vitamin D metabolism in rats.

In pregnant rats it has been possible to show that the distribution of cholecalciferol metabolites in their fetuses reflects the distribution of these metabolites in the blood. In these experiments, pregnant rats were maintained on a vitamin D deficient diet but were supplemented with radiolabelled cholecalciferol. The metabolites found were 25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol and, to a lesser extent, cholecalciferol. 1,25-Dihydroxycholecalciferol was not detected in fetal tissues, despite the ability of fetal kidney homogenates to hydroxylate 25-hydroxycholecalciferol in C-1. Kidney homogenates of newborn pups were found to possess marked activity of 25-hydroxycholecalciferol-24-hydroxylase, which was retained even in hypocalcemic pups born to pregnant rats that were fed a low-calcium diet. Injection of radiolabeled cholecalciferol to newborn pups resulted in the formation of 25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol. 1,25-Dihydroxycholecalciferol was not detected. Tissues thought of as target organs for vitamin D (in pregnant rats), namely, intestine, kidney and bone, were found to contain none or very little 1,25-dihydroxycholecalciferol. Mammary glands obtained from lactating rats were found to contain mainly the unchanged vitamin.     

Synthesis of 1 alpha-hydroxy[7-3H]cholecalciferol and its metabolism in the chick.

1. 1 alpha-Hydroxy[7-3H]cholecalciferol (specific radioactivity of 2-Ci/mmol) was synthesized, and its metabolism in chicks studied. 2. 1 alpha-Hydroxy[7-3H]cholecalciferol was metabolized very rapidly in the chick to 1 alpha,25-dihydroxy[7-3H]cholecalciferol and to a metabolite less polar than 1 alpha-hydroxycholecalciferol. Intestine exhibited highest accumulation of 1 alpha-25-dihydroxy[7-3H]cholecalciferol, and liver exhibited highest accumulation of the non-polar metabolite. 3. Tissue uptake of 1 alpha-hydroxy[7-3H]cholecalciferol and its metabolites in chicks that were dosed continuously for 16 days with 1 alpha-hydroxy[7-3H]cholecalciferol did not exceed by very much that observed in tissues obtained from chicks that were dosed with a single injection of 1 alpha-hydroxy[7-3H]cholecalciferol 24 h before killing, except for liver and kidney. 4. Lowest accumulation of metabolites was noted in muscle and bone, and for the latter, highest uptake of 1 alpha,25-dihydroxy[7-3H]cholecalciferol was noted in the epiphysial periosteum and the metaphysis. 5. Formation of 1 alpha,24,25-trihydroxy[7-3H]cholecalciferol was not observed in the chicks that were dosed continuously with 1 alpha-hydroxy[7-3H]cholecalciferol, despite the fact that plasma calcium and phosphorus were normal and despite the presence of renal 24-hydroxylase activity. 6. The vitamin D status of the chicks did not appear to affect the metabolic profile of the administered 1 alpha-hydroxy[7-3H]cholecalciferol.     

Elevated plasma corticosterone decreases yolk testosterone and progesterone in chickens: linking maternal stress and hormone-mediated maternal effects

Despite considerable research on hormone-mediated maternal effects in birds, the underlying physiology remains poorly understood. This study investigated a potential regulation mechanism for differential accumulation of gonadal hormones in bird eggs. Across vertebrates, glucocorticoids can suppress reproduction by downregulating gonadal hormones. Using the chicken as a model species, we therefore tested whether elevated levels of plasma corticosterone in female birds influence the production of gonadal steroids by the ovarian follicles and thus the amount of reproductive hormones in the egg yolk. Adult laying hens of two different strains (ISA brown and white Leghorn) were implanted subcutaneously with corticosterone pellets that elevated plasma corticosterone concentrations over a period of nine days. Steroid hormones were subsequently quantified in plasma and yolk. Corticosterone-implanted hens of both strains had lower plasma progesterone and testosterone levels and their yolks contained less progesterone and testosterone. The treatment also reduced egg and yolk mass. Plasma estrogen concentrations decreased in white Leghorns only whereas in both strains yolk estrogens were unaffected. Our results demonstrate for the first time that maternal plasma corticosterone levels influence reproductive hormone concentrations in the yolk. Maternal corticosterone could therefore mediate environmentally induced changes in yolk gonadal hormone concentrations. In addition, stressful situations experienced by the bird mother might affect the offspring via reduced amounts of reproductive hormones present in the egg as well as available nutrients for the embryo.     

Maternal-perinatal interrelationships of vitamins D metabolism in rats

In pregnant rats it has been possible to show that the distribution of cholecalciferol metabolites in their fetuses reflects the distribution of these metabolites in the blood. In these experiments, pregnant rats were maintained on a vitamin D deficient diet but were supplemented with radiolabelled cholecalciferol. The metabolites found were 25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol and, to a lesser extent, cholecalciferol. 1,25-Dihydroxycholecalciferol was not detected in fetal tissues, despite that ability of fetal kidney homogenates to hydroxylate 25-hydroxycholecalciferol in C-1.Kidney homogenates of newborn pups were found to possess marked activity of 25-hydroxycholecalciferol-24-hydroxylase, which was retained even in hypocalcemic pups born to pregnant rats that were fed a low-calcium diet.Injection of radiolabeled cholecalciferol to newborn pups resulted in the formation of 5/25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol. 1,25-Dihydroxycholecalciferol was not detected.Tissues thought of as target organs for vitamin D (in pregnant rats), namely, intestine, kidney and bone, were found to contain none or very little 1,25-dihydroxycholecalciferol.Mammary glands obtained from lactating rats were found to contain mainly the unchanged vitamin.     

The functional metabolism of vitamin D in chicks fed low-calcium and low-phosphorus diets.

Radioactively labelled cholecalciferol was administered continuously to chicks that were fed normal, low-calcium and low-phosphorus diets. It has been possible to show that under such steady state conditions with regard to cholecalciferol, and mineral restriction, the animal reacts by increased accumulation of 1, 25-dihydroxycholecalciferol in the intestinal and the kidney cell, which was associated in the intestine with an increased calcium-binding activity. A similar accumulation of 1, 25-dihydroxycholecalciferol in bone was not noticed. It is proposed that the intestine and the kidney, but not bone, are the main target organs for cholecalciferol in the maintenance of calcium homeostasis, and that both calcium and phosphorus play a role in the regulation of the formation and subsequent function of 1, 25-dihydroxycholecalciferol.     

The role of thyroid and adrenal cortical hormones in the modulation of the gonadal function in birds

The role of the thyroid gland in modulating the gonad function depends on the functional state of the gonads. In sexually inactive (short-day's) male Japanese quails, thyroidectomy and thyroxine treatment prove ineffective. Thyroxine administered simultaneously with photo-gonadostimulation inhibits the maturation of the gonads: the testes decrease in weight, the metabolic clearance rate of testosterone accelerates, resulting in a decrease in the plasma level, and androsterone production increases. Photo-gonadostimulation of thyroidectomized quails shows down the growth of the testicles and decreases the plasma testosterone level. The latter change can be related to the inhibition of the secretion rate. Both thyroidectomy and thyroxine administration performed in mature male quail, cock, pigeon or Peking duck lower the testosterone plasma level. The loss of the testicular weight is more expressed in hyperthyroid than in normal quails, referring to the role of the increased thyroxine level in the seasonal (summer) gonadal involution. Thyroidectomy performed on sexually inactive (short-day's) female Japanese quails does not affect the ovarian structure, but 17 beta-oestradiol and testosterone plasma levels show a slight increase. Thyroxine administration is followed by a moderate increase in the size of the white follicles, and an increase of both the progesterone and the oestrogen concentrations. Photo-gonadostimulation of thyroidectomized quails causes an inhibition of the mechanism of ovulation without inhibiting the development of the yellow follicles. A similar phenomenon has been observed in mature quails and domestic fowls after thyroidectomy. In both cases, an unbalanced secretion of the sexual steroids occurs: the 17 beta-oestradiol plasma level declines, while the progesterone level increases. Simultaneous application of thyroxine and photo-gonadostimulation on female quails inhibits gonadal maturation: the growing of the yellow follicles slows down. In thyroxine-treated birds, the plasma level of all of the sexual steroids shows a considerable decrease, which can be attributed to a reduced secretion rate and increased metabolic clearance. In hatching turkeys, we failed to observe the increase of the T3 level described for other species, however, the T4 plasma concentration was increasing at the early period of hatching. The role of the thyroid hormones in the development of hatching has not been cleared up so far. Corticosterone administration shows a slight stimulating effect on the gonadal function of sexually inactive male and female Japanese quails.(ABSTRACT TRUNCATED AT 400 WORDS)     

Sex differences in the hydroxylation of cholecalciferol and of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol in rat liver.

The effect of sex hormones on hydroxylation of cholecalciferol ('vitamin D3') and of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol has been investigated in female- and male-rat livers. The mitochondrial cholecalciferol 25-hydroxylase and C27-steroid 27-hydroxylase activities were respectively 4.6- and 2.7-fold higher in female- than in male-rat livers. The microsomal 1 alpha-hydroxycholecalciferol 25-hydroxylase was 2.8-fold higher in male- than in female-rat liver. No significant difference was found in the microsomal 25-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol. Liver microsomes (microsomal fractions) from male, but not from female, rats also catalysed 1-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol. Injection of testosterone into female rats decreased the mitochondrial cholecalciferol 25-hydroxylase and C27-steroid 27-hydroxylase activities, but not to a statistically significant extent. Testosterone treatment had no effect on the microsomal hydroxylases in female-rat liver. Injection of oestradiol valerate to male rats resulted in increased activities of both mitochondrial hydroxylases to the same levels as those of control females, while the microsomal enzyme activities decreased. The present results indicate that sex hormones exert a regulatory control on the mitochondrial cholecalciferol 25-hydroxylase and C27-steroid 27-hydroxylase activities.     

Incorportion of oxygen-18 into the 25-position of cholecalciferol by hepatic cholecalciferol 25-hydroxylase.

The oxygen enzymically inserted as a hydroxy function by rat liver post-mitochondrial fraction into the 25-position of cholecalciferol to giver 25-hydroxycholecaliferol is derived exclusively from molecular O2. Therefore like the other two cholecalciferol hydroxylases, i.e. 25-hydroxycholecalciferol 1alpha-hydroxylase and 25-hydroxycholecalciferol 24-hydroxylase, the cholecalciferol 25-hydroxylase is also a mono-oxygenase ('mixed-function oxidase').     

The metabolism of cholecalciferol in the liver of Japanese quail (Coturnix coturnix japonica) with particular reference to the effects of oestrogen.

1. Studies were carried out in vitro with the livers of Japanese quail that had been fed from hatching on diets supplying their full requirements for vitamin D. 2. 25-Hydroxycholecalciferol was the major metabolite when liver homogenates of egg-laying female and oestrogen-treated quail of both sexes were incubated with [3H]cholecalciferol. 3. Very little 25-hydroxycholecalciferol was generated from liver homogenates of adult male and immature quail. Instead the cholecalciferol was converted into one or more compounds less polar than 25-hydroxycholecalciferol and into a number of highly polar metabolites, some of which were water-soluble. 4. Oestrogen not only stimulated the 25-hydroxylation of cholecalciferol but also protected both cholecalciferol and 25-hydroxycholecalciferol from degradation by the enzymic pathways active in immature and male birds. 5. These actions of oestrogen may be of physiological significance in relation to the high requirements of laying birds for 1,25-dihydroxycholecalciferol to support the intense metabolism of calcium associated with egg-shell calcification.     

Gonadal maturation and serum calcium levels in two teleosts,the hake and the killifish

• 1.1. The relationship between gonadal maturation and serum calcium levels was studied in hake, Merluccius gayi gayi, and killifish, Fundulus heteroclitus.
• 2.2. Sexually mature male and female hake were sampled in the field throughout the year. Serum calcium was higher in all sexually mature fish regardless of the season, indicating a gonadal effect on serum calcium levels.
• 3.3. Male killifish adapted to constant laboratory conditions showed no change in serum calcium at different stages of gonadal maturation. Castration also had no effect. However, clear relationships exist between testicular maturation and serum inorganic phosphate, percentage hematocrit and liver sizes.
• 4.4. Such species differences are discussed.

     

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

Summary 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.     

The molecular compression of dextran.

Three side-chain analogues of cholecalciferol (vitamin D3) modified at C-25, namely 25-fluorocholecalciferol, 24-dehydrocholecalciferol and 25-dehydrocholecalciferol, conceived as potential inhibitors of the cholecalciferol 25-hydroxylase have been prepared and tested in the rat. These compounds markedly diminish conversion in vivo of cholecalciferol into 25-hydroxycholecalciferol, but are not antagonists of vitamin D action, because they themselves possess significant biological activity in vivo. Each compound is capable of stimulating the intestinal transport of calcium and the mobilization of calcium from bone in vitamin D-deficient rats. Biological responses equivalent to those generated by a physiological dose of cholecalciferol (0.05 microgram) are produced, however, only when the analogues are administered at high doses (5-50 microgram). The biological activity of 24-dehydrocholecalciferol and 25-dehydrocholecalciferol is shown to result from conversion, in vivo, to the natural hormone, 1 alpha,25-dihydroxycholecalciferol, whereas 25-fluorocholecalciferol is metabolically activated in the rat by hydroxylation to 1 alpha-hydroxy-25-fluorocholecalciferol. This latter conversion is the first reported example of the 1 alpha-hydroxylation of a vitamin D compound lacking the 25-hydroxy group.     

The lack of relationships between vitamin D3 metabolites and calcium-binding protein in the eggshell gland of laying birds

The relationship of the metabolism of vitamin D3 and calcium-binding protein (CaBP) to calcium transport by the eggshell gland (ESG) was assessed in chickens. Plasma or ESG 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) and ESG CaBP were no different between periods of ESG inactivity and of shell calcification. A severe dietary calcium deficiency resulted in increased kidney 25-hydroxycholecalciferol-1-hydroxylase activity (542%), plasma and ESG 1,25(OH)2D3 concentrations (193 and 274%, respectively), but in decreased ESG CaBP (34%), associated with the production of poorly calcified eggs. Significant correlations were found between 25 hydroxycholecalciferol-1-hydroxylase, plasma 1,25(OH)2D3 and ESG 1,25(OH)2D3, but not between ESG 1,25(OH)2D3 and CaBP. Hens with a low shell density had a significantly lower (55%) ESG CaBP than those with high shell density, without any significant change in ESG 1,25(OH)2D3. Significant correlations were found between ESG CaBP and shell calcium. Total receptors for 1,25(OH)2D3 were lower in ESG than in the intestine. The results suggest that CaBP level and calcium transport in the ESG are not regulated by 1,25(OH)2D3.     

The relationship between vitamin D-stimulated calcium transport and intestinal calcium-binding protein in the chicken

1. The rapid stimulation of intestinal Ca²⁺ transport observed in vitamin D-deficient chicks after receiving 1,25-dihydroxycholecalciferol has necessitated a re-evaluation of the correlation hitherto observed between this stimulation and the induction of calcium-binding protein synthesis. By 1h after a dose of 125ng of 1,25-dihydroxycholecalciferol, Ca²⁺ transport is increased. This is at least 2h before calcium-binding protein can be detected immunologically and 1h before synthesis of the protein begins on polyribosomes, and thus the hormone stimulates Ca²⁺ transport before calcium-binding-protein biosynthesis is induced. 2. The maximum increase in Ca²⁺ transport observed after this dose of 1,25-dihydroxycholecalciferol (attained by 8h) is similar to that observed after 1.25–25μg of cholecalciferol, but the stimulation is only short-lived, in contrast with the effect observed after the vitamin. At later times after the hormone, however, when Ca²⁺ transport has declined to its basal rate, the cellular content of calcium-binding protein remains elevated. 3. Calcium-binding protein is synthesized on free rather than membrane-bound polyribosomes, which implies that it is an intracellular protein. 4. Rachitic chicks require the presence of dietary calcium for maximum stimulation of calcium-binding protein production by cholecalciferol. 5. These results suggest that calcium-binding protein is an intracellular protein, and that its synthesis may be a consequence of the raised intracellular calcium content of the intestinal epithelial cells resulting from 1,25-dihydroxycholecalciferol-stimulated Ca²⁺ transport. We propose that calcium-binding-protein synthesis is necessary for maintaining the stimulated rate of Ca²⁺ transport, which is initiated by other factors.     

The timing of gonadal development and moult in three raptors with different breeding seasons: effects of gender, age and body condition

Differences between species in breeding seasons are thought to be mediated through differences in their reproductive physiology. Little is known about how the timing and duration of gonadal maturation varies between raptor species, how the timing of moult relates to the gonadal cycle, whether the timing and degree of sexual maturation varies between juveniles and adults or whether body condition has a significant effect. To address these questions, data on gonadal size and moult for adults and juveniles of both sexes of three raptor species were extracted from the Predatory Bird Monitoring Scheme (based on birds found dead by members of the public). The three species, Sparrowhawk Accipiter nisus, Kestrel Falco tinnunculus and Barn Owl Tyto alba, have different ecologies – diurnal bird predator, diurnal mammal predator and nocturnal mammal predator, respectively. All are single‐brooded but have different breeding seasons. The duration of gonadal maturation was markedly different between the species. Barn Owls showed the earliest maturation and the latest gonad regression, and Sparrowhawks the latest maturation and earliest gonad regression. Kestrels were intermediate. In males of all species, the testes remained fully mature throughout their respective breeding seasons. In females, the ovaries remained partially mature throughout the breeding season. Moult started slightly earlier in Sparrowhawks than in Kestrels and coincided with gonadal regression in the two species. Although females of the two species started to moult earlier than males, moult duration was similar between the sexes. Barn Owls showed no distinct annual pattern of moult. In juveniles of all three species, the gonads were smaller than in adults throughout spring and started to mature later. Gonad size in birds that had starved tended to be smaller than in birds dying from other causes, but did not influence the difference in gonad mass between adults and juveniles and between seasons. Body condition had no effect on moult. Whilst ecology has led to the evolution of different breeding seasons, differences between species, and between adults and juveniles, are mediated through adaptive differences in their reproductive physiology.     

Studies on calciferol metabolism. VII. The effects of actinomycin D and cycloheximide on the metabolism, tissue and subcellular localization, and action of vitamin D3

It was originally postulated, primarily on the basis of experiments employing actinomycin D, that calciferol (vitamin D) mediated its characteristic physiological responses in the intestine via the activation of information stored in the intestinal genome. A more recent alternative hypothesis suggested that actinomycin D blocked the biological response to calciferol by inhibiting the mandatory metabolism of cholecalciferol to 1,25-dihydroxycholecalciferol. Presented in this paper are the results of recent experiments studying the effects of both actinomycin D and cycloheximide on the metabolism, subcellular localization, and action of cholecalciferol or its metabolites, 25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol. Actinomycin D was found to inhibit calcium transport stimulated by cholecalciferol or its metabolites without inhibiting their metabolism or localization in the target tissue, the intestinal mucosa. However, actinomycin D had to be administered in four doses at 2-hr intervals to block the stimulation of calcium transport by 1,25-dihydroxycholecalciferol. Actinomycin D was also found not to lower the renal levels of 25-hydroxycholecalciferol-1-hydroxylase, which were measured in vitro. In contrast, cycloheximide was found to inhibit the localization of the sterols in the intestine. Also cycloheximide lowered the renal enzyme levels which were measured in vitro following administration of the antibiotic in vivo. From these data it can be calculated that the 25-hydroxycholecalciferol-1-hydroxylase appears to have a $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of approximately 3 hr. Thus, the inhibition of intestinal calcium transport by these two antibiotics may in fact occur at two different target organs; cycloheximide by a lowering of the kidney levels of 25-hydroxycholecalciferol-1-hydroxylase and actinomycin D by blocking the action of 1,25-dihydroxycholecalciferol in the intestine.     

Reproductive cycle and gonadal development of the Atlantic sea urchin Arbacia punctulata in the Gulf of Mexico: changes in nutritive phagocytes in relation to gametogenesis

ABSTRACT

The annual reproductive cycle comprises steady gametogenic activities that synchronize gonadal maturation and spawning rhythms, which are important for aquatic organisms including marine echinoderms (Echinodermata, Echinoidea). In this study, we report the annual reproductive cycle, gonadal development, and changes in nutritive phagocytes (NPs, which accumulate nutrients in germ cells) in relation to gametogenesis of the Atlantic sea urchin (Arbacia punctulata, an edible echinoid) in the Gulf of Mexico. Monthly changes in gonadal development and maturation were observed morphologically and histologically. We calculated gonadosomatic index (GSI) and compared the stages of gonadal development in order to determine the NPs index, and characteristics of germ cells (eggs and sperm) during the annual reproductive cycle. According to GSI and histological analyses, gametogenic activities were classified into four stages of both sexes: mature (June–August), spent (September–November), recovery (December–March), and growing (April–May). The GSI values in both sexes were high during summer months. In males, testicular lobules were densely packed with sperm from June to August. In females, however, mature eggs first appeared in some ovaries in May, numerically increased from June to July, and decreased in August. During gametogenesis, on the other hand, NPs in both testes and ovaries were depleted from June to August. Collectively, our results suggest that the Atlantic sea urchin spawns during summer months in the Gulf of Mexico. This is the first report, to the best of our knowledge, on gonadal development and changes in NPs during the annual reproductive cycle of any Arbacia species in the Gulf of Mexico.