Modifications of pars intermedia cells of ovariectomized rats by oestrogen and progesterone

Abstract

The effects of the ovarian steroids, oestradiol benzoate (EB), and progesterone (P) on the cells of pars intermedia (PI) from chronically ovariectomized rats (CHR-OVX) were analyzed by qualitative and quantitative electron microscopy (EM) at different intervals after steroid injection. The PI cells of CHR-OVX are rich in secretory granules but poor in organelles related to hormonal synthesis. Twenty-four h after EB administration the cells exhibited cytological features indicative of an increased synthetic activity. These included hypertrophy of rough endoplasmic reticulum, cisternae, a moderately developed Golgi complex, and newly formed granules. These features were also observed in PI cells 48 h after EB administration. Thirty-two and 56 h after the treatment, the PI cells showed signs of both increased synthetic and secretory activity. Thus, it was possible to observe a well-developed rough endoplasmic reticulum, and Golgi apparatus, numerous electron-lucent vesicles, and secretory granules in contact with the cell membrane. However, no exocytotic figures were observed. Progesterone administration resulted in considerable modifications of the ultrastructural features of PI cells also indicative of increased synthetic and secretory activity. The greatest modifications were observed in the mornings with changes that were 12 h out of phase with respect to those observed with EB.Quantitative estimations of the variation in the content of secretory granules of PI cells fully confirmed the qualitative observations described above. The serum \g=a\-MSHconcentrations in ovariectomized rats was found to be incresed 24 h after administration of a single dose of EB and thereafter serum MSH exhibited high levels in the afternoon, whereas the values in the morming were lower. In spayed rats, progesterone injection also resulted in an increase of the serum MSH concentration, but with high levels in the mornings and low levels in the afternoons. In conclusion, EB and P induce modifications in the levels of \g=a\-MSHas well as in the ultrastructural changes of the PI cells.The effects of ovarian steroids on -MSH secretion is well documented. It has been shown that CHR-OVX rats diminished their -MSH pituitary con¬ tent when thev were treated with EB or as compared with control rats receiving oil (Taleisnik & Tomatis 1969, 1970. More recently, it was de¬ monstrated that serum -MSH levels showed a circadian rhythm after EB or treatment. Thus, when EB was injected to CHR-OVX rats, a rise in serum -MSH levels was observed with maximum values at 5 p.m. and morning values similar to those of control animals. also raised serum a-MSH, but the high values were found in the morning, whereas afternoon levels were low (Celts 1977a,b). Similar results were found by other authors (Thody et al. 1981).In this study we are interested in determining the effects of these two ovarian steroids on the morphological organization of PI cells. An electron microscopy study was performed to illustrate and quantify the modifications of PI cells induced...

Evaluation of pituitary gland anatomy and histopathologic findings in clinically normal horses and horses and ponies with pituitary pars intermedia adenoma

“…25 Interestingly, results of 1 study 26 indicate that tumors of the intermediate lobe of the pituitary gland developed in Syrian hamsters treated with estrogens, whereas long-term administration of estradiol benzoate to ovariectomized rats increased concentrations of serum α-melanocyte-stimulating hormone because of enhanced synthetic activity of pars intermedia cells. 27 In humans, hyperadrenocorticism commonly develops in women of childbearing age, but may develop at any age. 28 In horses, females are also affected more frequently with PPIA than males.…”

The effect of the blockade of α-melanocyte-stimulating hormone on LH release in the rat

“…These results show that the blockade of \g=a\-MSHinhibits LH release and the next ovulation in rats treated with PLG or with concentrated antiserum against \g=a\-MSH, through a blockade of progesterone of adrenal origin. Journal of Endocrinology (1993) 137,[197][198][199][200][201][202] The role of a-melanocyte-stimulating hormone (a-MSH) in the control of different aspects of reproduc¬ tion has been studied extensively (Cehovic, 1965;Tomatis & Taleisnik, 1968;Runnenbaum et al 1973;Celis, 1975Celis, , 1985Aide & Celis, 1980;Khorram et al l9Ua,b;Volosin & Celis, 1984, 1988Ferreira & Celis, 1986;Durando et al I9c\9a,b;Scimonelli & Celis, 1990).…”