Morphology and physiological significance of parathyroid glands in reptilia.

Adult reptiles possess one or two pairs of parathyroid glands that have been shown in many species to derive from the third and fourth pharyngeal pouches, respectively. Up to five pairs may develop during early embryonic life. Excess glands may involute during late embryogenesis. The location of the parathyroid glands differs in the various species. As a general rule, they lie just anterior to the heart, the anterior pair (parathyroid III) being associated with the carotid artery, the posterior pair (parathyroid IV) with the aortic arch. In snakes, however, the anterior pair (parathyroid III) is associated with the carotid artery near the angle of the jaw. As shown by light microscopy and, to a lesser extent, by electron microscopy, the parathyroid parenchyma comprises secretory cells which may form dark and light variants, occasional oxyphil cells, and stellate cells. They are arranged in cords separated by connective tissue containing a capillary network. Parathyroid secretory cells often form follicles which might be the result of degeneration. Degeneration may occur as a form of involution during winter in species undergoing seasonal changes. The product of parathyroid cells, the parathyroid hormone, is responsible for the maintenance of blood calcium concentration. The sites of action--bones, kidneys, intestine, endolymphatics, and dermal skeleton--are not well understood or not investigated. In some turtles, parathyroid hormone is not the (main) factor for the regulation of calcium homeostasis.

Amphibian parathyroids: morphological and functional aspects.

Amphibians living partially or totally in a terrestrial environment are the first tetrapods to possess parathyroid glands. Purely aquatic amphibians and amphibian larvae lack these endocrine glands. The parathyroids develop at the time of metamorphosis. The parathyroid glands in caecilians consist of a single cell type, that of urodeles may be composed of basal (supporting) cells and suprabasal (chief) cells, and that of anurans of small and large chief cells. Parathyroid glands of caecilians and anurans lack connective tissue, blood vessels, and nerves. The parathyroid cells become activated in response to decreased blood calcium concentration and undergo changes indicating increased parathyroid hormone secretion. Increased blood calcium concentration suppresses secretory activity. Usually, parathyroidectomy elicits hypocalcemia in most amphibians. Such operations have no effect in lower urodeles. Parathyroid hormone administration provokes hypercalcemia in most amphibians. The parathyroids of caecilians have not been studied in detail. The urodeles and anurans exhibit seasonal changes in the parathyroid glands. These changes may be initiated by environmental stimuli such as light, temperature, or alterations in blood calcium levels caused by natural hibernation.

Molecular evolution of shark C-type natriuretic peptides.

C-type natriuretic peptides (CNP) of varying length were isolated from the atrium or ventricle of a shark, Lamna ditropis and their amino acid sequences were determined. Although the sequence of Lamna CNP was highly homologous to those of other CNPs sequenced to date, the Lamna CNP-41, the longest CNP identified in this study, has one amino acid replacement from those of Triakis scyllia and Scyliorhinus canicula, and three amino acid replacements from that of Squalus acanthias. The degree of similarity of CNP molecules coincides well with their systematic positions in the cladogram of elasmobranchs; Lamna, Triakis and Scyliorhinus belong to the same order, but Lamna and Squalus belong to different orders. The facts that Lamna and Triakis are in different suborders but Triakis and Scyliorhinus are in the same suborder and have identical CNP-41, also support this evolutionary implication.

Anuran Calcitonins are Diverse in Lower Vertebrates.

We investigated the nucleotide sequences of cDNA fragments coding calcitonin from ultimobranchial glands in 2 species of urodelans (1 salamander and 1 newt) and 4 species of anurans (1 toad and 3 frogs) by the reverse transcription polymerase chain reaction (RT-PCR) method and rapid amplification of cDNA ends (RACE)-PCR method. The salamander and newt calcitonins were each 97% and 94% similar to the lungfish and caiman calcitonins that we have already reported, in the amino acid sequences. However, anuran calcitonins were not only dissimilar (63-81%) to the lungfish and caiman calcitonins but also diversified (59-91%) even among anurans. The sequence identity of toad calcitonin was always low (59-66%) among anurans.

Unpaired Ultimobranchial Glands of the African Lungfish, Protopterus dolloi.

The ultimobranchial glands of juvenile African lungfish (Protopterus dolloi) (14 individuals; total body length 25-205 mm) were immunohistochemically examined. In individuals larger than 36 mm, one ultimobranchial gland was close to the left afferent branchial arteries. The topography of the ultimobranchial gland was similar to that of salamanders and sharks, but not to teleosts. With body growth, the ultimobranchial gland was vascularized and the parenchymal cells were gradually immunostained with anti-calcitonin antibody. In all individuals examined, the ultimobranchial gland existed only on the left side of the pharynx. These observations are discussed from a phylogenetic viewpoint.

Nucleotide sequences of reptile calcitonins: their high homology to chicken calcitonin.

The calcitonin genes of four species of reptiles (Reeve's turtle, rat snake, grass lizard, and spectacled caiman) were amplified from the genomic DNA, as well as from the mRNA of the ultimobranchial glands of the former three species, by the polymerase chain reaction (PCR) method, and were sequenced. Among several primer sets, only one primer set synthesized from the chicken calcitonin gene was compatible with those of the reptiles. The nucleotide sequences of the reptile calcitonin genes were highly homologous with that of chicken calcitonin (100% for turtle, 99% for caiman, 96% for lizard and 93% for snake). The products amplified from mRNA by the RT-PCR method matched completely those from genomic DNA in the turtle, snake and lizard.

Amino acid sequence of sardine calcitonin and its hypocalcemic activity in rats.

A novel calcitonin (CT) was isolated from the spotlined sardine, Sardinops melanostictus. The primary structure of sardine CT was determined as follows: H-Cys-Ser-Asn-Leu-Ser-Thr- Cys-Ala-Leu-Gly-Lys-Leu-Ser-Gln-Glu-Leu-His-Lys-Leu-Gln-Ser-Tyr-Pro-Arg- Thr- Asn-Val-Gly-Ala-Gly-Thr-Pro-NH2. This amino acid sequence was different from that of salmon CT in 4 amino acid residues at positions 8th, 21th, 27th and 29th. As judged by the international method of CT bioassay, hypocalcemic activity of sardine CT was calculated as 4156 IU/mg. When compared for durability of CTs, it was found that sardine CT was significantly more potent than that of salmon CT. This is the first report of CT from a marine species of teleost.

Vitamin D3-induced calcemic and phosphatemic responses in the freshwater mud eel Amphipnous cuchia maintained in different calcium environments.

Vitamin D3 (100 ng 100 g body weight-1 day-1) was administered intraperitoneally (i.p.) to the freshwater mud eel Amphipnous cuchia kept in artificial freshwater, calcium-free freshwater, low-calcium freshwater (0.2 mmol/l CaCl2) or calcium-rich freshwater (13.4 mmol/l CaCl2) for 15 days. Analyses of serum calcium and phosphate levels were performed on days 1, 3, 5, 10 and 15 after the beginning of the experiment (six eels from each group at each interval). Administration of vitamin D3 elevated the serum calcium [maximum elevation occurred at day 10 in artificial freshwater (vehicle: 10.55 +/- 0.298, vitamin D: 13.90 +/- 0.324), low-calcium freshwater (vehicle: 11.17 +/- 0.220, vitamin D: 12.98 +/- 0.297) and calcium-rich freshwater (vehicle: 11.24 +/- 0.373, vitamin D: 14.24 +/- 0.208) whereas it occurred at day 5 (vehicle: 8.42 +/- 0.253, vitamin D: 11.07 +/- 0.328) in calcium-free freshwater] and phosphate levels [maximum elevation at day 15 in artificial freshwater (vehicle: 4.39 +/- 0.105, vitamin D: 5.37 +/- 0.121), calcium-free freshwater (vehicle: 4.25 +/- 0.193, vitamin D: 5.12 +/- 0.181), low-calcium freshwater (vehicle: 3.93 +/- 0.199, vitamin D: 5.28 +/- 0.164) and calcium-rich freshwater (vehicle: 3.77 +/- 0.125, vitamin D: 5.46 +/- 0.151)] of the fish maintained in the above mentioned environmental media, but the responses were more pronounced in the fish kept in calcium-rich media.

Ultimobranchial glands in the teleost (Plecoglossus altivelis ryukyuensis): special references to changes of gland volume with maturation.

In lower vertebrates, the bone-mineralizing hormone "calcitonin" is secreted from ultimobranchial glands, which assume various shapes, e.g., follicles, cellular masses, or cell strands. Histological observations support the view that in some teleosts, the glands increase in size when females maturate. We determined the exact volume of the gland in juveniles and adult males and females of a teleost, Ryukyuayu (Plecoglossus altivelis ryukyuensis). Furthermore, we examined plasma Ca, Na and K levels. In this species, the gland was fundamentally composed of a single follicle. The gland volume was converted to numerical data under a certain condition. It thus became clear that the value of the follicle wall was significantly increased only in maturing and mature females with high plasma Ca levels and that the value of the lumen did not show any statistically significant changes during growth and maturation.

Influence of prolactin administration on the ultimobranchial body and parathyroid glands of the freshwater snake, Natrix piscator.

The effects of ovine prolactin (10 I.U./100 g body wt) on the ultimobranchial body and parathyroid glands were investigated in Natrix piscator for 15 days. The ultimobranchial body of the prolactin treated specimens depicts signs of increased activity whereas the parathyroid glands exhibit reduced activity.

The non-effect of parathyroidectomy in the aquatic limbless newt (Apoda, Amphibia).

In the aquatic limbless newt, Typhlonectes compressicauda (Apoda, Amphibia), serum Ca levels of parathyroidectomized newts were no lower than for the control newts at 1 week after the operation. In this species, the parathyroid glands may not be functional in raising the serum Ca levels.

[Physiology of vertebrates under micro-gravity with special reference to the Ca metabolism].

On April 12, 1961, Major Yurii A. Gagarin of the former-U.S.S.R. Air Force circled the Earth in a spacecraft named "Vostok", a word which means "east". He spent 1 hour and 48 minutes in space. Since then, the U.S.S.R. and the U.S.A. have sent many astronauts into space. In one case, the stay in space exceeded a year in length, reaching 438 days. Through these experiences, it became clear that micro-gravity caused various problems in human physiology. One of the most serious problems was the loss of Ca from bones, as a result of the negative expenditure of Ca. Under 1G on the ground, bone absorption and bone formation proceed in accordance. Under micro-gravity, however, this balance is broken. Although this phenomenon has been widely analyzed from the viewpoint of molecular biology as well, studies to clarify the mechanism that causes the disorder of Ca metabolism in bones have just started. At present, no perfect treatment to prevent the loss of Ca from bones is available.

No hypocalcemic action of Stannius corpuscle homogenates in rats.

1. Serum Ca level of goldfish administered with homogenate of the corpuscles of Stannius (CS) taken from 1/3 seawater-acclimated goldfish was significantly lower than that of the control goldfish up to 2 hr after administration. 2. Serum Ca, Mg, Pi, Na and K levels of rats administered with CS homogenates of freshwater eels, 1/3 seawater-acclimated goldfish, or seawater-inhabited wrasse were not statistically different from those of control rats during the 3 hr investigation. 3. It was concluded that in rats, CS homogenates did not decrease the serum mineral levels under the present conditions.

Urine calcium concentrations in bullfrog tadpoles kept in tap water or high calcium environment, with special reference to ultimobranchialectomy.

1. Urine calcium concentrations were determined in intact and ultimobranchialectomized bullfrog tadpoles kept in tap water (Ca: 8.5 and 19.7 mg/100 ml), urine calcium levels did not show significant increases. 3. In ultimobranchialectomized tadpoles, hypercalciuria concomitant with the rise in serum calcium levels in recognized under both conditions of high calcium water and tap water. 4. It was suggested that in bullfrog tadpoles ultimobranchial glands do not exert effective influences on the renal handling of calcium.

Hypocalcemic potency of the ultimobranchial gland in some urodelan amphibians.

The hypocalcemic potencies of the ultimobranchial glands of two urodelans, Onychodactylus japonicus and Hynobius nigrescens, were studied; according to the rat bioassay, their calcitonin values (MRC) were 30 and 18 mU/kg body wt, respectively. Various organs other than the ultimobranchial gland were also assayed in rats to see whether they had any hypocalcemic potency. However, the ultimobranchial gland was the only organ examined with detectable hypocalcemic potencies in these urodelans. The hypocalcemic potencies of urodelan ultimobranchial glands are one order lower than those reported in the other vertebrate classes, contrasting with the potencies of anuran ultimobranchial glands. The biological significance of this low potency is discussed.

Effects of anesthesia on the electrolyte concentrations in blood and coelomic fluid of the earthworm, Pheretima communissima.

Sodium, potassium, calcium and magnesium concentrations in blood and coelomic fluid of Pheretima communissima under various methods of anesthesia or in the unanesthetized condition were determined. All electrolyte concentrations determined in ethanol-anesthetized earthworms were not significantly different from those in unanesthetized earthworms. Thermal (warming, cooling) anesthesia, urethane and chloretone brought about increases or decreases in some electrolyte concentrations in the blood or coelomic fluid. However, not all electrolytes responded similarly to a method of anesthesia.

Renal handling of phosphate, calcium, sodium, and potassium in intact and parathyroidectomized Rana pipiens.

Renal excretion of phosphate, calcium, sodium, and potassium in intact and parathyroidectomized male Rana pipiens was studied by renal clearance techniques using 14C-inulin. In intact frogs, 57% of filtered phosphate, 60% of filtered calcium, 97% of filtered sodium, and 89% of filtered potassium was reabsorbed by the renal tubules. Following parathyroidectomy, the rate of reabsorption of phosphate became significantly higher than that of the intact frog, and the relative phosphate clearance (fractional excretion) decreased. These changes corresponded with a gradual rise in serum phosphate values. There was no major effect on excretion patterns of calcium, sodium, or potassium after parathyroidectomy. These results suggest that in frogs the parathyroid glands strongly influence phosphate excretion patterns but have little effect on the excretion of calcium, sodium, or potassium.