Ultrastructure and chemical composition of calcite urinary calculi in Chinese swamp buffalo.

Four urinary calculi, derived from Chinese swamp buffalo, were studied by using qualitative chemical analysis, X-ray diffraction, scanning electron microscopy and qualitative energy dispersive (electron probe) microanalysis. Qualitative chemical analysis showed that the predominant ions were calcium and carbonate with small amounts of magnesium and ammonium. X-ray diffraction confirmed that the calculi were primarily composed of calcium carbonate (calcite). On ultrastructural examination, three apparently distinct structural regions were identified in the calculi: outer large laminations; cavities containing variable numbers of small spheres and rods; and large spheres. There did not appear to be material that acted as a nidus and all regions, on qualitative electron probe analysis, contained primarily calcium with trace amounts of magnesium, phosphorus, potassium and chloride. It was concluded that calcite calculi in Chinese swamp buffalo are probably formed through a process of asynchronous layering and that nidus formation may not be necessary. Moreover, the ultrastructure of the calcite calculi is similar to that reported for siliceous calculi in ruminants and this suggests that similar factors may be involved in their formation.

Effect of cycloheximide on the ovine corpus luteum: the role of granules in the secretion of progesterone.

Cycloheximide (3 mg/h) was infused into the corpus luteum of the sheep via a side branch of the ovarian artery. The concentration of progesterone in the peripheral plasma and the luteal tissue decreased after the infusion. Ultrastructural studies showed that cycloheximide caused inhibition of the formation and secretion of densely stained granules in the luteal cells. The results provide further evidence that progesterone bound to protein is secreted by the luteal cell in the form of granules.

Ultrastructural study of granules in the corpora letea of several mammalian species.

The ultrastructure of the corpora lutea of the goat, cow, rabbit, pig and guinea pig have been examined at a stage when progesterone was being secreted by the luteal cells. Densely staining granules, 0.2micrometer in diameter, are present within the luteal cells of all the species examined. Granules were detected in the extra-cellular spaces of the corpora lutea of the goat, cow and pig, but not of the rabbit or guinea pig. The luteal cells of the various species have the same basic structure but differ in the amounts of lipid and forms of smooth endoplasmic reticulum present. A common mechanism of hormone secretion, in granule form, is postulated for all luteal cells.

Granule secretion by the luteal cell of the sheep: the fate of the granule membrane.

The ultrastructure of the corpus luteum of the sheep has been examined at the mid-stage of the estrous cycle when progesterone secretion is active. Secretory granules are associated with the secretion of this hormone, and the evidence indicates that the granule membrane becomes incorporated into the plasma membrane during exocytosis. Further evidence of this process has been obtained from studies on the uptake of horseradish peroxidase by the luteal cells.

Secretion of granules by the luteal cells of the sheep and the goat during the estrous cycle and pregnancy.

The fine structure of luteal tissue from sheep and goats at the mid-stage of the estrous cycle and during pregnancy was examined. At the mid-stage of the estrous cycle, when the corpus luteum of both species is secreting progesterone, the ultrastructure of the luteal cells is similar in that granule secretion is prevalent. In late pregnancy, the corpus luteum of the sheep produces very little progesterone and there is an absence of granule secretion. In the pregnant goat, the production of progesterone from the corpus luteum is high and there is plentiful evidence of granule formation and secretion.

Influence of ruminal and plasma osmotic pressure on salivary secretion in sheep.

The osmotic pressure of the rumen contents and also of the blood was altered by intraruminal administration of water or hypertonic solutions. It was found that alterations in osmotic pressure were accompanied by inverse changes in the flow rate of mixed saliva. Intravenous infusion of hypertonic solutions, causing elevation of the osmotic pressure of the blood without affecting that of the rumen, also caused a reduction of salivary secretion rate. The flow rates of both parotid and residual saliva were affected. When strongly hypertonic solutions of sodium or potassium salts were infused into the rumen, or sodium salts or urea were infused into the blood, the concentration of those substances increased in the saliva. Other treatments had little effect on salivary composition.

Absorption of 125I-labelled sheep growth hormone in single proximal tubules of the rat kidney.

Techniques of kidney micropuncture and electron microscope autoradiography have been used to study the uptake of 125I-labelled sheep growth hormone (GH) in rat renal proximal tubules. After microperfusion of a proximal tubule with 125I-labelled GH, the transport of label by the tubular epithelium was studied autoradiographically at selected times up to 1 h. The sequential transfer of labelled material from tubule to microvilli, then to small and large apical vacuoles and finally to lysosomes followed the pattern of absorption that has been described for other proteins. Evidence of lysosomal degradation of the transported protein was obtained from studies in vitro; lysosomes isolated from the renal cortex rapidly converted 125I-labelled GH to products of lower molecular weight. In addition to the absorptive pathway through the intracellular vacuolar apparatus is appeared that there was also an alternative pathway, less well defined, whereby GH could be absorbed without being degraded.