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Biomedical subjects

R W Steger

Publications and source records attributed to R W Steger.

At least 19 recordsLinked to original sources
PubMed1992

Acute effects of delta-9-tetrahydrocannabinol on dopaminergic activity in several rat brain areas.

In this work, we examined the acute effects of two doses of delta-9-tetrahydrocannabinol (THC) on several pre- and postsynaptic biochemical measures of dopaminergic activity in the striatum, limbic forebrain, and hypothalamic-anterior pituitary area of adult male rats. The exposure to a low dose of THC (0.5 mg/kg bw) decreased the number of striatal D2 dopaminergic binding sites, but did not affect their affinity. Treatment with a higher dose of THC was ineffective. In addition, both doses decreased the number of D1 dopaminergic binding sites in the limbic forebrain without changing their affinity. We did not find any changes in the dopamine (DA) or L-3,4-dihydroxyphenylacetic acid (DOPAC) content, or in the DOPAC/DA ratio, in either the striatum or limbic forebrain. THC treatment produced a dose-related decline in plasma prolactin (PRL) levels. Furthermore, both the basal and DA-inhibited in vitro release of PRL were reduced in animals exposed to THC in a dose-dependent manner. This inhibitory effect of THC on PRL release was accompanied by a decreased DOPAC/DA ratio in medial basal hypothalamus that, in turn, may be a result of the fall in PRL levels rather than a direct action of the drug. These data show that acute exposure to THC can alter brain dopaminergic neurotransmission. Our results suggest that the reduction of PRL release following THC exposure, both in vivo and in vitro, might be elicited by a direct action of THC on the pituitary.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1992

Catecholamines stimulate testicular testosterone release of the immature golden hamster via interaction with alpha- and beta-adrenergic receptors.

Several lines of evidence suggest that catecholamines are involved in the regulation of the development of the testis. We have therefore investigated the ability of testicular parenchyma (decapsulated pieces of testes) from 18 to 20-day-old golden hamsters to respond to catecholaminergic stimuli in vitro. Norepinephrine and epinephrine, as well as the beta-receptor agonist isoproterenol and the alpha-adrenoreceptor agonist phenylephrine were able to significantly stimulate testicular testosterone production. Dopamine and serotonin were not effective. The stimulatory action of norepinephrine on testosterone production was dependent on the concentration. In incubations of testes with human chorionic gonadotropin (hCG) and norepinephrine, no synergistic effects on testosterone release were observed. The stimulatory effect of norepinephrine could be partially blocked by incubation with beta-receptor antagonist propranolol, or with alpha-receptor antagonist prazosin, while a combination of propranolol and prazosin completely inhibited the norepinephrine-induced testosterone production. Moreover, isoproterenol and phenylephrine in combination stimulated testosterone more than either drug did alone. Measurements of concentrations of norepinephrine and epinephrine in testicular homogenates revealed higher values for these catecholamines than in the plasma, implying that catecholamine levels in the interstitial spaces of the testis might be in the range of concentrations effectively stimulating testosterone production in vitro. This suggests that in the immature testis of the golden hamster, catecholamines acting through both alpha- and beta-adrenergic receptors may be potent physiological stimulators of testosterone production.

Animals↗
PubMed1979

Hypothalamic-pituitary function in the old irregularly cycling rat.

Older irregularly cycling and younger regularly cycling rats exhibited similar increases in LH levels 1, 2 and 3 wks after ovariectomy, but FSH reached higher levels in the older than in the younger rats after ovariectomy. Neither the ability of 5 microgram/kg estrogen to suppress gonadotropin levels nor the capability of larger doses of estrogen (250 micrograms/kg) and/or progesterone (10 mg/kg to trigger an LH release were altered with age. LH release from the pituitary in response to exogenous gonadotropin releasing hormone (GnRH) was attenuated in ovariectomized older rats, but was partially restored after estrogen and/or progesterone priming. The FSH levels after GnRH treatment were greater in the estrogen primed aged that in estrogen-primed younger rats. The disruption of regular cycles in older rats may be due to a lack of a neural signal for gonadotropin release rather than a failure of the hypothalamus to respond to the positive feedback effect of estrogen or the failure of the pituitary to respond to GnRH.

Aging↗
PubMed1979

Pattern of follicular growth and steroidogenesis in the ovary of aging cycling rats.

Prior to the cessation of reproductive cycles, older female rats exhibit irregular and prolonged cycles due to alterations in the hypothalamic-pituitary-ovarian axis. In order to evaluate the age-related changes in the ovary, the histology, and estradiol, testosterone and progesterone concentrations within the ovaries of mature regular cycling (4--5 mo. old) and older irregular cycling (10--11 mo. old) rats were examined. At estrus, the number of non-atretic growing follicles (150--300u in diameter) was greater in the mature than in the older rats (18 +/- 1.5 vs 4.5 +/- 1.4). However, the number of preovulatory follicles on proestrus did not differ (6.0 +/- 1.2 vs 5.5 +/- 0.6). Estradiol, testosterone and progesterone concentrations on proestrus in mature rats averaged 38.8 pg, 56.1 pg, and 1.0 ng/ml of ovary, respectively. In the older proestrous rat, only estradiol was altered, increasing to 124.3 pg/mg. In addition, many of the preovulatory follicles within the aged ovary were larger (greater than 600u in diameter) than those within the mature ovary. On the day of estrus virtually all preovulatory follicles ovulated in the mature rat, whereas large follicles, less than or equal to 600u in diameter, remained in the older ovary. In addition, estradiol levels remained elevated and ovarian cysts were observed in the aged ovary. Thus, in the older irregular cycling rat, 1) pre-ovulatory follicles develop, but many do not ovulate; 2) these non-ovulatory follicles form ovarian cysts which remain within the ovary. The number of cysts may increase with age until a polycystic ovary develops and the rat enters a constant estrous state.

Aging↗
PubMed1979

Gonadotropin binding and testicular function in old rats.

Serum testosterone levels, testicular LH binding and the spermatogenic cycle were analyzed in rats 4 and 22 mo of age. With age, serum testosterone levels decreased from 3.2 to 0.63 ng/ml serum. There was no age related decline in testicular LH binding or changes in the spermatogenic cycle.

Aging↗
PubMed1978

Patterns of sex steroid and gonadotropin secretion in aging female rats.

Serum estradiol, progesterone, LH, and FSH were determined by RIA in 20- to 30-month-old constant estrous (CE), irregular pseudopregnant (PP), and anestrous (AS) female rats and from 4- to 5-month-old cycling female rats. Disruption of the estrous cycle in aging rats was associated with major changes in secretion of pituitary gonadotropins and ovarian steroids. None of the old rats, in contrast to the young rats, showed cyclic changes in any of the hormones studied. Serum progesterone was much higher in the PP than in the other two old groups, serum estradiol averaged somewhat higher in the CE than in the other two aged groups, and all four hormones were lower in the AS rats than in any other group. Basal serum FSH values were higher in the old CE rats than in either of the other old age groups and were slightly higher than in young rats on the afternoon of proestrus or morning of estrus. Serum FSH values were lower in the old PP and AS rats than in young rats on the afternoon of proestrus or morning of estrus. Serum FSH values were lower in the old PP and AS rats than in young rats on the afternoon of proestrus or morning of estrus. Serum values in the old CE rats were about the same as in young rats on the morning of proestrus or estrus, about the same in old PP rats as in young rats during diestrus, and were undectable in old AS rats. Since the ovaries of old rats are capable of near normal function under appropriate gonadotropic stimulation, it is concluded that the major cause for cessation of regular estrous cycles in old rats lies in altered hypothalamo-pituitary function.

Aging↗
PubMed1978

Gonadotrophin regulation in the lactating rat.

Post-partum lactation in the rat is associated with follicular quiescence and an attenuation of gonadotrophin secretion. The present study demonstrates that the lactating rat responds to exogenous LH-releasing hormone (LH-RH) in a manner similar to dioestrous rats. Oestrogen priming increases the LH and FSH response to LH-RH to a smaller degree in ovariectomized, lactating, than in non-lactating, ovariectomized rats. Pituitary LH levels throughout lactation did not seem to be related LH-RH-induced LH release. A diminished post-castration rise in both LH and FSH, and a diminished positive feedback response to oestrogen administration were also observed and may indicate a disruption of gonadotrophin regulation at both the hypothalamic and the pituitary level.

Animals↗
PubMed1978

Role of FSH in regulating granulosa cell division and follicular atresia in rats.

The effects of PMSG on the mitotic activity of granulosa cells and atresia of large folicles in 24-day-old rats were examined. The results showed that the labelling index (1) decreased in atretic follicles parallel with a loss of FSH binding, and (2) increased in hypophysectomized rats treated with FSH. It is concluded that FSH stimulates granulosa cell divisions and that atresia may be caused by reduced binding of FSH to the granulosa cells.

Animals↗
PubMed1977

Sequential changes associated with the degeneration of preovulatory rat follicles.

In 26-day-old rats, follicles capable of ovulation were present 48 h after PMSG injection and they degenerated if not exposed to an ovulating dose of HCG. In such follicles 125I-labelled LH bound to the thecal and granulosa cells. By 60 h after PMSG, LH binding to the granulosa cells was reduced by 46% although these follicles retained their ability to ovulate. LH binding to the granulosa cells was lost in most follicles by 72 h and ovulation could not be induced. The thecal cells still possessed LH binding sites at 72 h after PMSG. HCG stimulation of these follicles resulted in disruption of the granulosa and the invasion of blood cells into the antrum.

Acid Phosphatase↗
PubMed1977

Scanning electron microscopy of human female reproductive tract and amniotic fluid cells.

Scanning electron microscopy was used to examine surface ultrastructural characteristics of cells of the epithelium of female reproductive tract, cervical mucus, and amniotic fluid cells. The female epithelium undergoes hormone-dependent cyclical morphological alterations in cell shape, apical microvilli, ciliation, and secretory patterns. The frequency distribution of ciliated cells varies in different parts of the female reproductive tract and different segments of the same organ. In the endocervix, a few ciliated cells are randomly distributed. The density of ciliated cells is variable in several areas of the endometrium. The sparse distribution of ciliated cells in the central portion of the uterine wall may indicate a possible implantation site. According to surface ultrastructure of cells, three segments are noted in the uterotubal junction: cornual endometrium, interstitial tubal epithelium, and transitional area. The vaginal epithelium is made of flat polygonal cells with interdigitating borders and a fine interlacing network of microridges. After the menopause, the microridge pattern and distinct cell borders are lost or severely modified. Two types of fibrous structures can be found in cervical mucus: a) microfibrils that vary in diameter from 500 to 1,500 A and from bundles or networks, and b) long, thick fibers that vary in diameter from 0.5 to 5 micrometer run parallel to each other, and appear to be made up of microfibrils. Amniotic fluid cells, derived from amniotic epithelium and fetal ectoderm, consist of non-nucleated and nucleated cells with extensive microplicae.

Amniotic Fluid↗
PubMed1976

Effect of photoperiod on gonadotropin releasing hormone-induced LH release in the immature rat.

Female rats raised from birth under a light/dark (LD) or constant light (LL) regimen were given injections at either 24, 29, 33 or 35 days of age of either 5 IU PMSG or 0.1 ml saline. Two days following PMSG or saline injection, the rats were given injections of either 1,000 ng synthetic gonadotropin releasing hormone (GnRH) or 0.1 ml saline. Blood samples were taken before and 20 min after injection for LH determinations. PMSG caused a rise in basal LH levels, which was greater in LL than in LD animals. GnRH administration resulted in an LH surge in both LD and LL rats at all ages tested. The LL animals released greater amounts of LH in response to GnRH than did LD animals. In PMSG-primed animals there were no differences in the GnRH-induced LH surge due to either age or photoperiod. It is concluded that PMSG and LL enhance the pituitary's response to GnRH.

Age Factors↗
PubMed1976

Ultrastructure of testes and excurrent ducts in the bonnet monkey (Macaca radiata).

The testes and excurrent ducts of four bonnet macaques (Macaca radiata) were examined using scanning and transmission electron microscopy. The three layers of contractile and connective tissue composing the tunica albuginea, and the multilayered tunica propria of the seminiferous tubules were similar to that of man. Spermatids project from the epithelium or are found free in the lumen. The stages of the cycle of the germinal epithelium in the bonnet macaque were similar to that in other macaques. The epithelium of the rete testis consisted of thin brush-bordered cells, whereas the epithelium of the efferent ducts consisted of tall, prismatic or cylindrical cells lined by kinocillia or short stereocilia and basal cells. The height of the epididymal epithelium and lumen diameter was maximal in the caput region and minimal at the cauda. Spermatozoa were found among clusters of stereocilia. The epithelium of the vas deferens showed gradual transition from the stereocilia covering typical of the epididymis to that of a shorter, apical microvilli covering.

Animals↗
PubMed1976

Development of gonadotrophin-binding sites in the immature rat ovary.

There was a temporal relationship between ovarian development and the sites to which 125I-labelled gonadotrophins became bound. Labelled human LH and FSH bound uniformly to 5- and 15-day-old ovaries. At 21 days, heavy FSH and light LH binding was observed over the granulosa cells increased at Day 33 and again at Day 38. Quantitative determination by gamma-ray spectrophotometry of binding to ovarian sections showed that LH binding gradually increased with advancing age, but FSH binding remained relatively constant between Days 5 and 33 with a significant increase between Days 33 and 38.

Age Factors↗