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Biomedical subjects

K Shirama

Publications and source records attributed to K Shirama.

30 records · Page 2Linked to original sources
PubMed1978

Induction of persistent estrus by constant light: effects of neonatal constant light and Harderian gland function.

The effect of constant light on the age at onset of persistent estrus was compared in rats exposed to constant light since birth (LL-0) and those exposed beginning at 70 days of age (LL-70). Persistent estrus occurred about 27 days later in the LL-0 rats than in the LL-70 rats. Exposure to LL for just the 1st 15 days of life (LL-0-15) and then subsequent exposure to LL at 71 days also delayed the induction of persistent estrus. Neonatal injection of a Harderian gland (HG) homogenate to LL-0-15 rats reduced the age of vaginal opening and 1st estrus and reduced the delayed onset of persistent estrus caused by the neonatal LL. Harderianectomy of LL-0 or hematoporphyrin injections in LL-0-15 rats had no effect on the onset of LL-induced persistent estrus.

Animals↗
PubMed1976

Influence of monoamine oxidase inhibitor on the induction of persistent estrus by androgen in the rat.

Effect of monoamine oxidase inhibitor (MAOI) on the induction of persistent estrus by testosterone propionate (TP) was studied in Wistar strain female rats. Daily treatment with MAOI for the 1st 10 days of life accelerated the occurrence of persistent estrus in rats given TP at 8 days of age. The onset of persistent estrus occurred at 57.3+/2.0 days of age in these animals compared to 92.6+/5.5 days in saline-treated controls. The contribution of hypothalamic monoamines to the induction of persistent estrus by TP treatment in neonatal rats will be discussed.

Age Factors↗
PubMed1976

Recurrence of estrous cycles in the light-induced persistent estrous rats by reserpine.

Effect of continuous illumination (LL) on ovarian functions was compared at various ages between the rats exposed to LL from 70 days of age (LL-70) and exposed to LL from the day of birth (LL-0). LL-0 rats retained corpora lutea in their ovaries in higher incidence than LL-70 rats. Effect of reserpine on the restoration of cyclicity was studied in LL-0 and LL-70 rats shortly after they became persistent-estrous. LL-0 rats restored cyclicity in higher incidence than in LL-70 rats.

Animals↗
PubMed1975

Pinealectomy and sexual rhythm in female rats.

The role of the pineal gland in inducing and maintaining the persistent estrus of rats exposed to continuous illumination was examined. Under the cyclic illumination, the pinealectomy or sham-operation revealed no effect on the estrous cycle, although weights of the ovaries, adrenals and hypophysis were slightly but definitely greater in the pinealectomized animals. In rats exposed to the continous illumination immediately after pinealectomy or sham-operation, both groups exhibited the persistent estrous states soon after the change of lighting condition. In these rats, neither the degree of persistent estrus nor the organ weights a autopsy showed any significant difference between the groups. Moreover, the pinealectomy could not alter the incidence of estrous in persistent estrous rats which had been established already by the continuous illumination.

Animals↗
PubMed1975

Correlation between sexual maturation and induction of persistent estrus by continuous illumination.

The rats brought up under continuous illumination from the neonatal day persist in the rhythmic estrous cycle for long time and do not easily reveal so-called continuous vaginal estrus. On the contrary, immature rats at about 30 days of age show the persistent estrus soon after exposure to continuous illumination as well as adult rats. The purpose of this paper was to examine the relation of the age placed under continuous illumination and the time required to reach the persistent estrus. As the results, it was found that the younger rats need proportionally the longer time to reach the persistent estrus; the rats which were transferred into continuously illuminated environment at 0 (group A), 5 (group B), 10 (group C), 15-16 (group D) and 30 (group E) days of age required a mean time of 132.1 +/- 8.4, 126.8 +/- 8.9, 89.7 +/- 6.2, 91.5 +/- 3.8 and 70.3 +/- 3.0 days after birth to reach the persistent estrus, respectively. In the present data, a significant difference was seen between group B and C. Though all rats were killed after the same length of persistently estrous periods, actual endocrine level appeared to differ among the groups; the rats required longer time to reach the persistent estrus had smaller ovaries and adrenals.

Age Factors↗
PubMed1975

Inhibitory effect of 5-hydroxytryptophane on the induction of persistent estrus by androgen in the rat.

Effects of monoamines or its precursors on the induction of persistent estrus by testosterone propionate (T.P.) were studied in Wistar strain female rats. Daily treatment with 5-hydroxytryptophane (5-HTP) for the first 10 days of life delayed the occurrence of persistent estrus in rats given T.P. at 4 days of age. The onset of persistent estrus occurred in this group of animals at 67.1+/-2.5 days of age compared with 45.1+/-1.4 days of age for the saline treated control group. The role of hypothalamic monoamines in contributing to the induction of persistent estrus by T.P. treatment of neonatal rats is discussed.

5-Hydroxytryptophan↗
PubMedDate not supplied

Postnatal development of the harderian gland in the rabbit: light and electron microscopic observations.

We have investigated the development of the Harderian glands of Japanese white rabbits from birth to 4 months of age. Although two types of secretory cells comprise the glandular epithelium of the pink and white lobes in fully developed glands, the time of neonatal appearance is different between the two. Cells consisting of the pink lobe first appear on the third day of life, while cells of the white appear around seventh day of life. The ultrastructure of the Harderian glands from 1-week-old rabbits resembles that of adult animals. The gland can be divided into three parts on the basis of their epithelial cell composition at the electron microscopic level. The respective parts are composed of: (1) one type of cells with large vacuoles (pink lobe), (2) one type of cells with small vacuoles (white lobe), and (3) two types of cells with large and small vacuoles (pink-white mixed portion). The relative number of plasma cells per 1 mm2 is low in both pink and white lobes during early postnatal life. However, in adult animals, the white lobe has a larger number of plasma cells than the pink lobe. These results suggest the possibility that the white lobe participates in the immune system more than does the pink.

Animals↗
PubMedDate not supplied

A direct effect of the pineal on the accessory sex organs in light deprived male rats.

One day after surgery groups of pinealectomized and sham-pinealectomized animals were placed in continuous darkness, and killed 0, 20, 40, 60, 80 and 100 days later. The data revealed that the sham-pinealectomized group exposed to constant darkness differs from pinealectomized group by showing lower dihydrotestosterone (DHT) concentrations, bw, accessory sex organ wt and levator ani muscle wt. No statistically significant differences were found in plasma LH, FSH and testosterone concentrations or pituitary or testes wt. The results indicated that the accessory sex organ wt were not correlated with the plasma gonadotropin and testosterone levels but they were with DHT. The data are consistent with the idea that some pineal principle acts directly on accessory sex organs in the rat.

Animals↗
PubMedDate not supplied

Influence of pinealectomy on circadian patterns of plasma luteinizing hormone, follicle-stimulating hormone, testosterone and dihydrotestosterone in the male rat.

The effect of pinealectomy on the circadian periodicity in plasma gonadotropins (LH and FSH), testosterone (T) and dihydrotestosterone (DHT) was investigated in adult male rats maintained under conditions of 12 h light/12 h dark (light on 06:00-18:00 h). Animals were killed at 3 hour intervals over 24 hours by decapitation. Plasma concentrations of LH, T and DTH (but not FSH) were found to exhibit significant circadian variations as determined by analysis of variance. No distinct LH or T nadir was recorded but peaks were observed at 09:00 h. Peak DHT values were recorded near the middle of the dark period. Pinealectomy resulted in an altered daily LH and T rhythmicity, and also in an abolished DHT rhythmicity. The fact that there was no significant increase in mean gonadotropin levels at 50 days after pinealectomy suggests that the pineal regulates the timing of gonadotropin secretion rather than the quantity. Since pinealectomy was found to abolish the circadian rhythm of DHT but not of T, we deduced that the pineal may also be responsible for the rhythmic conversion of T to DHT.

Animals↗