Scanning electron microscopy of the ovary in the house musk shrew, Suncus murinus.

The structure of the house musk shrew (Suncus murinus) ovary, prepared by the Osmium-DMSO-Osmium method, was examined with a scanning electron microscope. Many ovarian follicles in various stages of development can be seen in the musk shrew ovary, but fully matured follicles (Graafian follicles) are never observed. In the inner layer of zona granulosa of the preantral follicles, the follicular cells containing a large amount of glycogen deposition in the cytoplasm are observed. Folded and collapsed zona pellucida surrounding the remnant of the degenerated oocyte, which is thought to be a residual form of atretic follicle, is observed in a small, crypt-like depression on the surface of the ovary where it has been split by cracking.

Response of interstitial cells of the testes in the house musk shrew, Suncus murinus L., to various gonadotropins.

Testicular interstitial cells of the house musk shrew culture in vitro released testosterone in response to ovine LH with a quite similar dose response relationship to that found in the cells of rats. The dose response curves suggested that a single testicular cell of the shrew has the same potency to secrete testosterone as that of the rat. In the shrew as well as in the rat, neither ovine PRL added alone nor together with oLH could stimulate the testosterone release from testicular cells, although a very limited enhancement of testosterone secretion was observed in the cell cultured with a large dose of oFSH in both species.

Pituitary luteinizing hormone level in the male house musk shrew, Suncus murinus L., following castration and testosterone treatment.

The effect of castration and replacement therapy with testosterone propionate (TP) on the pituitary LH concentration and contents in the house musk shrew was investigated by using an in vitro bioassay for LH, the Rat Interstitial Cell Testosterone assay. The concentration and contents of LH increased slightly 10 days after castration, but decreased progressively thereafter to about a half of the pre-operation level by 90 days after the operation. The replacement with TP (100 micrograms/day) for 7 days significantly depressed LH contents when it was begun 10 days after castration, while the same treatment started immediately after or 30 days after the operation did not significantly affect the pituitary LH level. The feedback mechanism between the gonad and the pituitary may be slightly different in the shrew from that in other mammals. TP replacement, started immediately after castration, completely inhibited the decrease in the weight of male accessory sex organs in castrated shrews. In castrated animals when more than 10 days had elapsed after the operation, however, the decreased weight of the organs could not be fully restored by the TP replacement for 7 days.

[Growth and sexual maturation of the male house musk shrew (Suncus murinus)].

The sexual maturation in the male house musk shrew, Suncus murinus, was investigated by weighing gonads, accessory sexual organs and various other organs, and measuring testosterone concentrations in the plasma from birth to 50 days of age. The histological and histochemical studies of the testis were also carried out. Testicular weight increased markedly from 10 days of age. On 15 days of age, the activity of delta 5-3 beta-Hydroxysteroid dehydrogenase (HSD) was detected in Leydig cells. In accordance with an increase of HSD activity, the concentrations of plasma testosterone raised rapidly from 15 days of age and reached a peak on Day 30. Growth of prostate glands and seminal vesicles showed a sigmoidal pattern and their significant growth began from Day 25. Sperms were detected first in the seminiferous tubules on Day 28, and most tubules were filled with many sperms on Day 33. From these results, the beginning of sexual maturation, i.e. puberty, of the male shrew is considered to be around Day 25. The weight gain of testes, accessory sexual organs and the body became slower on Day 40. The male animal of Day 40 could mate and impregnate the female. Therefore, the male shrew seems to attain to the sexual maturity between days 35 and 40.

Fine structure of the lutein cell in the house musk shrew, Suncus murinus.

The ultrastructure of lutein cells during pregnancy and the post partum period was examined by transmission electron microscopy in the house musk shrew, Suncus murinus. Lutein cells on day 13 of pregnancy contained an extensive system of anastomosing tubules or cisternae of smooth ER and many enlarged mitochondria with numerous tubulovesicular cristae. From day 13 on, the number of small granules, possibly lysosomes, increased gradually. Between day 20 and 25, the loss of smooth ER began and elongated, or flattened mitochondria increased. Regressing lutein cells observed after parturition were characterized by abundant large dense bodies, bizarre mitochondria and a decrease in the amount of smooth ER. Unusual forms of mitochondria were always observed after day 5 of pregnancy. Two types could be distinguished; one, found frequently in the second third of pregnancy, was ring-, disc-, cup- or dumb-bell-shaped with tubulovesicular cristae, and the other, found exclusively in the last third of pregnancy and after parturition, was elongated, flattened and sometimes twisted. The paucity of lipid droplets was a characteristic feature of the lutein cells of this species. The significance of these ultrastructural changes of cellular organelles is discussed in relation to the ovarian and plasma levels of progesterone.

Mammary growth and plasma progesterone level during pregnancy in the house musk shrew, Suncus murinus Linnaeus.

The process of growth of the mammary gland and change in the plasma concentration of progesterone were investigated throughout the course of pregnancy (30 days) in the home musk shrew, Suncus murinus L. Development of the mammary gland of the musk shrew was limited during the first half of pregnancy. Extensive branching of ducts and conspicuous alveolar formation and a marked increase in the DNA content of the gland started between day 15 and 20 of pregnancy, and continued until term. Milk synthesis indicated by accumulation of the secondary fluid in the alveolar lumen and a sudden rise in the RNA/DNA ratio of the gland tissue seemed to be initiated 1 or 2 days before parturition. No lactose was detected in either the mammary tissue or milk of the house musk shrew. Plasma concentration of progesterone was very low until mid-pregnancy and began to rise after day 15, reaching a peak of 10--13 ng/ml around day 25. The steroid level started to fall shortly before parturition and returned to the basal level in post-parturient animals. Ovariectomy interrupted pregnancy in some animals, but not in others. When pregnancy was maintained, the mammary development and the plasma level of progesterone were normal.