Increases in calbindin D 28K mRNA in the uterus of the domestic fowl induced by sexual maturity and shell formation

Uterine concentrations of calbindin D 28K mRNA were measured in immature pullets and laying hens by dot-blot hybridization using a [32P]cRNA probe prepared from the calbindin cDNA. In immature pullets, estrogen increased the calbindin mRNA level and the plasma concentration of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. When testosterone was administered with estrogen there was a further increase in calbindin and its mRNA and an increase in the free 1,25-(OH)2D3 index calculated as the ratio of the molar concentrations of total 1,25-(OH)2D3 and vitamin D-binding protein (DBP). In laying hens the uterine concentration of calbindin mRNA was low 4 hr after ovulation, but increased most markedly 12 and 18 hr later, when shell calcification took place. Calbindin concentration remained unchanged during the different stages of egg formation but was much higher in laying hens than in pullets treated with sex steroids. Suppression of shell formation by premature expulsion of the egg decreased the concentrations of calbindin mRNA and uterine calbindin and the free 1,25-(OH)2D3 index in the plasma. A concomitant increase in calbindin and its mRNA was observed at resumption of shell formation in hens previously laying shell-less eggs. Withdrawal of food for 44 hr decreased the uterine concentration of calbindin and its mRNA without a change in the free 1,25-(OH)2D3 index in the blood. It is concluded that the synthesis of uterine calbindin is stimulated primarily at sexual maturity and at calcification of the first shell by transcriptional processes. The daily increase in calbindin mRNA associated with shell formation and the absence of a concomitant change in calbindin concentration suggest that post-transcriptional processes exist and that stimuli other than the sex steroid or the 1,25-(OH)2D3 are involved in regulation of calbindin synthesis in the uterus.

Pineal melatonin rhythms and the timing of puberty in mammals

The direction of change in daylength provides the seasonal time cue for the timing of puberty in many mammalian species. The pattern of melatonin secretion from the pineal gland transduces the environmental light-dark cycle into a signal influencing the neuroendocrine control of sexual maturation. The change in duration of nocturnal melatonin secretion is probably the key feature of the melatonin signal which conveys daylength information. This information may also be used by neuroendocrine axes controlling seasonal changes in pelage colour, growth and metabolism. The mechanism of action of melatonin on neuroendocrine pathways is unknown. Although the ability to synthesize and secrete melatonin in a pattern that reflects the duration of the night may not occur until the postnatal period, the rodent and ovine foetus has the ability to respond in utero to photoperiodic cues to which its mother is exposed in late gestation. Transplacental passage of maternal melatonin is likely to be the mechanism by which photoperiodic cues reach the foetus. Species which do not exhibit seasonal patterns of puberty, such as the human, also secrete melatonin in a pattern which reflects the environmental light-dark cycle, but they do not respond reproductively to the seasonal melatonin information.

Effect of hypo and hyperprolactinemia on the testicular maturation of Wistar rats during puberal transition

In Wistar rats, the structural and metabolic organization of the testis was influenced by the blood concentration of prolactin. The androgen dependent enzyme activities in plasma as well as in testis were higher under hyperprolactinemia and lower under hypoprolactinemia, as induced by bromocriptine. While prolactin had direct effect on the testicular functions, bromocriptine seemed to exert its influence through blocking hypophysial prolactin.

Effects of chronic LHRH-a + 17-methyltestosterone or LHRH-a + testosterone therapy on oocyte growth in the striped mullet (Mugil cephalus)

The striped mullet (Mugil cephalus) exhibits a restricted spawning season and matures only once per spawning cycle. In vivo monitoring of ovarian maturation of individual females during the season reveals that timing of full maturity varies. A small percentage of females that mature early can be induced to spawn and will remature. Such females can be spawned a second time within the same season. Chronic administration of luteinizing hormone-releasing analog (LHRH-a) + testosterone results in accelerated egg growth. The majority of females undergoing this therapy mature at least a month before control fish. When these females are induced to spawn, a higher percentage remature and can be spawned again. The double spawnings of both control and LHRH-a + testosterone-treated females occur without any appreciable loss in egg quality. Administration of LHRH-a + 17 alpha-methyltestosterone essentially inhibits egg growth. Steroid profiles from females undergoing this therapy exhibit a significant drop in circulating testosterone and estradiol 17 beta, compared to control and LHRH-a + testosterone-treated females. Hypotheses for the poor performance of this therapy are discussed.

Estradiol influences on pattern of gonadotropin secretion in bovine males during the period of changed responses to estradiol feedback in age-matched females

When ovaries are removed prior to puberty, administration of exogenous 17 beta-estradiol (E2) decreases concentrations of luteinizing hormone (LH) below that of ovariectomized heifers receiving no E2. Subsequent to the time age-matched intact heifers reach puberty, exogenous E2 increases secretion of LH in ovariectomized heifers above that of ovariectomized heifers receiving no E2. The hypothesis that E2 would inhibit gonadotropin secretion in bovine males during the time E2 no longer inhibited gonadotropin secretion in age-matched bovine females was tested. Males (n = 12) and females (n = 12) were gonadectomized at 241 +/- 3 days of age, and half of each sex (6 males and 6 females) were administered a 27-cm E2 implant. An additional group of males (n = 6) and females (n = 6) remained intact and served as controls. Blood samples were collected (to quantify LH and follicle-stimulating hormone [FSH]) from all animals at 15-min intervals for 24 h at 1, 7, 13, 17, 21, 25, 29, 33, 37, and 43 wk after gonadectomy. Additional blood samples were collected twice weekly from control females to monitor progesterone and onset of corpus luteum function (451 days of age). E2 inhibited frequency of pulses of LH (p less than 0.01) and decreased mean concentration of LH and FSH (p less than 0.01) at Week 1 in gonadectomized males treated with E2 compared to gonadectomized males not administered E2.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis of proteoglycans and hyaluronic acid by long-term cultures of testicular cells from immature and pubertal rats

Long-term cultures of somatic testicular cells derived from immature and pubertal rats were used to study the synthesis of proteoglycans (PG) and hyaluronic acid (HA). Labelled PG and HA in the culture medium, membrane-associated and intracellular pools were characterized by gel filtration, ion exchange chromatography and selected enzymatic and chemical treatments. Somatic cells synthesize a PG containing both heparan and chondroitin/dermatan sulfate (CS/DS) chains and a PG containing only CS/DS chains. No major qualitative changes in the type of PG were observed in cells derived from immature and pubertal animals. However, significant age-dependent differences in the cell distribution pattern of PG and HA were determined. This may have implications in the regulation of spermatogenesis.

Quantification of reproductive changes and nutrient requirements of broiler breeder pullets at sexual maturity

1. 480 Broiler breeder pullets, kept in individual cages, were subjected to different rates of increase in food allocation during the period 18 to 30 weeks of age. From 80 g food/bird d at the start of the experiment, the 5 treatments comprised linear weekly increments in food allocation to reach a maximum of 150 g/bird d at 21, 23, 25, 27 or 29 weeks of age respectively. 2. Body weight, liver weight, fat pad weight and alimentary tract weight were influenced by the rate of increment in food allocation. 3. Rate of development of the oviduct and the ovary was not influenced by these treatments. 4. Although the amount of fat and protein contained in the liver increased most rapidly on the treatments where 150 g/bird d was attained first, by 25 weeks of age there were no meaningful differences in these two variables between treatments. It is unlikely, therefore, that a high protein intake during this period would allow sufficient protein or energy to be stored in the liver to sustain a higher egg output later in the laying period. 5. It is concluded that the amount of protein required by a broiler breeder pullet for maintenance and for growth during the pre-laying period is about 10 g/bird d.

In-vitro development of zygotes from superovulated prepubertal and mature gilts

Ten prepubertal and 8 mature gilts were superovulated with PMSG and hCG, and inseminated with fresh boar semen. Zygotes were surgically recovered from oviducts 54-60 h after hCG. One and 2-cell zygotes were randomly allotted to Medium PL (modified BMOC-3 supplemented with 0.1 mM-EDTA and 1.5% BSA) or Medium G (Medium PL without pyruvate or lactate). Eggs were washed twice in medium, and placed in microdrops of medium overlaid with silicon oil for culture in an humidified 5% CO2, 5% O2, 90% N2 environment, then observed daily for 6 days. Development of eggs was dependent (P less than 0.001) on the interactive effects of age of gilt (prepubertal versus mature) and medium type (PL versus G) used in culture. A greater proportion of eggs cultured in Medium G developed further than did eggs in Medium PL (P less than 0.001). Additionally, a greater proportion of eggs from mature gilts developed further than did eggs from prepubertal gilts (P less than 0.02). We suggest that these results provide evidence that zygotes resulting from superovulation regimens of prepubertal gilts do not possess the same capacity for in-vitro development as do zygotes from pubertal gilts.

[Growth of girls and boys at puberty]

Growth at puberty varies according to age and individual maturity. Changes in height and weight of girls (aged 10 to 16 years) and boys (aged 11 to 17 years) which participate in a follow-up study at northern metropolitan Santiago, Chile, are described. Sexual maturity seems more determinant than chronological age on weight and height at puberty. For instance height of the whole sample of boys from 12 to 15.5 years of age ranged from 141 to 164 cm in contrast to 147 to 160 for those of the same age range but in the third stage of public hair development (Tanner). Sexual maturity should be taken into account for appropriate growth evaluation at puberty.

Development of the seminiferous tubules after neonatal hemicastration in the boar

Development of the prepubertal seminiferous tubules of the right testis was characterized morphometrically every 14 days from 10 to 122 days of age in intact boars (I) and boars hemicastrated (HC) on Day 10 of life from two herds (Trial 1 and Trial 2). Comparisons were made between the remaining testis of Group HC boars and one testis in Group I boars. By 38 days of age seminiferous tubule length in Group HC boars was double (P less than 0.0001) that in Group I boars. Seminiferous tubule length did not differ between trials within treatments. The diameter of the seminiferous tubule was similar in Group HC and I boars but was greater (P less than 0.05) in Trial-1 than Trial-2 boars from Day 80 to 122 of life. Relative mass (mass of tissue/body mass) of Sertoli cells became 2-fold greater (P less than 0.0001), in Group HC than in one testis of Group I boars by 38 days of age and this difference was maintained throughout the experimental period. The relative mass of Sertoli cells was greater (P less than 0.05) in Trial-1 than Trial-2 boars within each treatment between 80 and 122 days of age. The relative mass of gonocytes was similar for all groups and treatments of boars. By 122 days of age the relative mass of spermatogenic cells was greater (P less than 0.05) in Group HC than in one testis of Group I boars and greater (P less than 0.01) in Trial-1 than Trial-2 boars within each treatment. Onset of spermatogenesis was first observed at 80 and 94 days of age in boars in Groups HC and I, respectively. Development of seminiferous tubule lumen was first observed at 94 and 108 days of age in boars in Groups HC and I respectively. Seminiferous tubule lumen, taken as a measure of fluid secretion of the Sertoli cells, occupied a greater (P less than 0.01) portion of seminiferous tubule in Trial-1 than Trial-2 boars within each treatment at the end of the experimental period. It is concluded that neonatal hemicastration of boars rapidly caused a compensatory seminiferous tubule elongation apparently due to Sertoli cell proliferation and an earlier onset of spermatogenesis. However, the gonocytes do not proliferate until they transform into spermatogonia.

Development of the testicular interstitium after neonatal hemicastration in the boar

Development of the prepubertal interstitium of the right testes was characterized every 14 days from 10 to 122 days of age in intact boars (I) and boars hemicastrated (HC) at 10 days of age from two herds (Trial 1 and Trial 2). Comparisons were made between the remaining testis of Group-HC boars and one testis in Group-I boars. The relative mass (mass of component/body mass) of interstitium was 151% greater (P less than 0.001) in Group-HC than Group-I boars by 52 days of age. The relative mass of interstitium was greater (P less than 0.01) in Trial-1 than Trial-2 boars within each treatment from 80 to 122 days of age. The relative mass of interstitial space was 76% greater (P less than 0.05) in Group-HC than in one testis of Group-I boars by 52 days of age and greater (P less than 0.05) in Trial-1 than Trial-2 boars within each treatment from 80 to 122 days of age. The relative mass of Leydig cells was 254% greater (P less than 0.0001) in Group-HC than Group-I boars by 52 days of age and remained greater (P less than 0.05) in Group-HC than Group-I boars from 52 to 122 days of age. By 52 days of age the relative mass of Leydig cell nuclei and cytoplasm was 235% and 265% greater (P less than 0.0001) in Group-HC than Group-I boars, respectively, and both remained greater (P less than 0.05) in Group-HC than in Group-I until 122 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Roles of prepubertal androgen, estrogen or androgen plus prolactin on androgen-induced proliferative response of seminal vesicles in adult mice

Male mice castrated on day 0 after birth were pretreated daily with testosterone propionate (TP, 4 micrograms/g body weight), 17 beta-estradiol (E2, 0.2 micrograms/g body weight) or vehicle for 21 days starting from day 20. In another experiment, male mice were castrated on day 25; two pituitaries from 60-day-old females were immediately grafted under the capsule of the left kidney in one group. The castrated mice with or without grafts were pretreated daily with TP (4 or 20 micrograms/g body weight) for 36 days starting from day 25, and the left kidney was removed on day 60. Daily TP injections (4 micrograms/g body weight) were started again at 30 days after the end of pretreatments to examine androgen-induced proliferation, and incorporation of 5-[125I]iodo-2'-deoxyuridine into the whole seminal vesicles was used as an index of proliferation. In the neonatally castrated mice, both TP and E2 pretreatments given during the prepubertal period significantly increased seminal vesicle weight even long after the end of the pretreatments. However, androgen-induced proliferative response found in the neonatally castrated adult mice (poor response; long duration with a low peak) was changed to that found in mice castrated at adulthood (good response; short duration with a high peak) by the TP pretreatment only but not at all by the E2 pretreatment. In the mice castrated on day 25, a pharmacological dose of TP or TP plus hyperprolactin could not enhance or change the adult castration type of androgen-induced proliferation induced by physiological prepubertal androgens, although both treatments significantly enhanced the prepubertal growth of the seminal vesicles.

Puberty-affecting synthetic analogs of urinary chemosignals in the house mouse, Mus domesticus

Endocrinologically- and socially-dependent volatile constituents of female mouse urine, identified in a previous study, were tested for their capability to accelerate puberty and extend the estrous period in young females. Several volatile ketones advanced puberty by approximately three days and extended the period of vaginal cornification in 55-75% of exposed females. High High concentrations of these substances were capable of overriding the known puberty-delaying chemosignals. Volatile cyclic enol ethers were also effective in extending estrus, but not puberty acceleration.

Changes in pancreatic beta cell function during growth and reproductive maturity of rats

An attempt has been made to study the changes, if any, in the efficiency of pancreatic beta cell function at different ages using one experimental model. For this, pancreatic islets were isolated from albino rats of 3, 8, 12 and 36 weeks of age and challenged with various concentrations of glucose (11.0, 16.7 and 22.2 mM). Significantly higher rate of glucose stimulated (pro)insulin biosynthesis was seen in the islets from 3 week old rats as compared to the islets obtained from 8, 12 and 36 week rats. On the other hand, immunoreactive insulin release was observed to be highest from islets of 8 week old rats followed by that of 12, 36 and 3 week old ones.

Gonadal hormones influence the emergence of cortical function in nonhuman primates

The role of gonadal hormones in the maturation of the orbital prefrontal cortex (ORB) was studied in normal male and female rhesus monkeys, monkeys given ORB lesions at 50 days of age, and female monkeys given androgen at different ages. Monkeys were tested on an object discrimination reversal task at 75 days of age. Gender influenced the performance of monkeys on the task during normal development and after ORB lesions. Normal males made fewer errors than did normal females. Females treated with androgen performed similarly to normal male monkeys. ORB lesions produced deficits in male monkeys and in females given androgen during late prenatal or early postnatal life, but not in normal females. These findings suggest that gonadal hormones may play an inductive role in the differentiation of higher cortical function in nonhuman primates.

Physiology of puberty

Adolescence represents the period of important somatic changes which lead to sexual maturation, pubertal growth and active functions of reproduction. Mean ages of onset of puberty are 10.9 and 11.2 in girls and boys respectively. Menarche occurs at a mean age of 13.4 yr and may be related to a critical weight. In boys, testicular growth above 4 cm2 or 4 ml is the first clinical sign of gonadal pubertal maturation. In girls, the first sign is the budding of the breast. At onset of puberty, the hypothalamus after a "quiescent" period resumes a marked pulsatile secretion of gonadotrophin-releasing hormone, leading to an increased secretion of pituitary gonadotropins which in turn stimulate the gonadal functions, i.e. the secretion of testosterone or estradiol and maturation of the spermatogenesis or the ovarian follicle. Neuroendocrine factors which probably control the onset of puberty are numerous: cerebral adrenergic and/or dopamine neurotransmitters, endogenous opioids, melatonin from the pineal gland. Gonadal maturation (gonadarche) is preceded in the infant by a post-natal surge of luteinizing hormone and at age 7 to 8 yr by an adrenal maturation (adrenarche).

Growth and sport

In order to investigate sport's influence on growth during puberty, we examined 398 boys 10-16 yr old. 192 of these subjects had been playing football as a competitive sport, and 206 were considered as controls, having never practised sports regularly. Both groups were divided into prepubertal (with testicular volume less than or equal to 2.5 cc) and pubertal, with the latter further divided into the following chronological and bone age groups: 10-11.99, 12-13.99, 14-16 yr. In these subjects we evaluated auxological-anthropometric and biological maturity characteristics and endocrine parameters (cortisol, dehydroepiandrosterone sulphate, testosterone). No significant difference was found between prepubertal athletes and controls concerning anthropometric and biological maturation parameters, whereas testosterone basal levels were significantly lower (p less than 0.05) and DHEAS values were significantly higher (p less than 0.05). Pubertal football players were significantly taller than controls (particularly at 14-16 yr chronological age), with a greater biacromial diameter after 12 yr chronological and bone age and thinner skinfolds at 12-13.99 chronological and bone age. They were more advanced in all biological maturation parameters i.e. pubic hair, testicular volume and bone age, particularly those subjects playing football for the greatest number of years and training time. In pubertal football players the increase in DHEAS (p less than 0.05) already seen in prepubertals is also combined with a significant increase in testosterone (p less than 0.0001) and cortisol (p less than 0.05). Thus football players DHEAS is already higher during prepuberty and this increase chronologically precedes the advance in all the auxological-maturative parameters typical of our pubertal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet serotonin levels and gonadal hormones in rats

The role of gonadal hormones in the control of platelet serotonin levels was studied by evaluating the effect of sexual maturation in rats of both sexes and the time-course of changes following gonadectomy performed either prepubertally or on sexually mature animals. In males, platelet serotonin levels remained fairly stable during sexual maturation as well as during the whole postgonadectomy period monitored (four months). In females, somewhat higher values of platelet serotonin levels in adult than in sexually immature animals were found (9%, p less than 0.001, N = 34). A slight decrease of platelet serotonin (10-18%, p less than 0.05) was observed following ovariectomy of sexually mature females, but it was of transient nature. When females were ovariectomized prepubertally a tendency towards permanently lower platelet serotonin levels was noticed. These results suggest that gonadal hormones have no major role in the control of platelet serotonin levels in rats, although a subtle hormonal modulation of this platelet variable in females may exist.

Reproduction in the Indian mouse-tailed bat, Rhinopoma hardwickei hardwickei (Chiroptera, Rhinopomatidae)

At and near Agra, in Uttar Pradesh, India, R. h. hardwickei had a strictly defined annual reproductive cycle. Although many females were inseminated during late February to mid April, ovulation was not recorded until 11 March. Progressively more females ovulated and conceived during the following weeks until the end of April and released one ovum from either of the ovaries with nearly equal frequency. A single conceptus was carried in the ipsilateral uterine cornu during each cycle. The gestation period was 95-100 days. Births occurred between the second week of June and the end of July. Lactation lasted at least 20 days. Females attained sexual maturity at an age of 8.5-9.0 months. Males took at least 16-17 months to attain sexual maturity. Females were segregated during lactation; during the rest of the year, males and females lived together.

Changes in growth hormone (GH) secretion and in growth during puberty

During normal adolescent development in males testosterone induces the adolescent growth spurt, at least in part, by increasing GH production via an increase in the amplitude of the peaks of GH which are released, and not by increasing the frequency of GH pulses. Testosterone and estrogen administration at low or modest doses to individuals with the capacity to produce GH causes GH production and IGF-I levels to increase. Testosterone given to GHD patients does not increase either of these factors. In addition, there may be two actions for growth promotion by testosterone. One unequivocally results from an increase in GH production in the presence of low or modest levels of testosterone. A direct action on bone growth is probably present also, as reflected by the growth promoting effect of oxandrolone, a weak androgen, in boys with CDGA in the absence of increased GH production.

Vasoactive intestinal peptide regulates cholesterol side-chain cleavage cytochrome P-450 (P-450scc) gene expression in granulosa cells from immature rat ovaries

Vasoactive intestinal peptide (VIP), a neuropeptide present in ovarian nerves, has been previously shown to induce synthesis of the side-chain cleavage cytochrome P-450 enzyme which catalyzes the conversion of cholesterol to pregnenolone (the rate-limiting step in progesterone synthesis). In the present study we demonstrate, by means of a bovine 3'-specific P-450scc cDNA probe, that this VIP effect is exerted at least partially at the level of gene expression in cultured granulosa cells that were isolated from estrogen-primed, immature rats. The size and level of the 2.0 kilobase P-450scc mRNA species was assessed by Northern blot analysis, while the translatability of this mRNA was assayed by immunoisolation of the 35S-labeled P-450scc precursor protein translated from total RNA of control and stimulated granulosa cells. FSH was much more effective than VIP at increasing P-450scc mRNA concentrations in cultured granulosa cells, whereas secretin treatment was ineffective. The results suggest that, like FSH, the stimulatory effect of the neuropeptide VIP on ovarian progesterone secretion involves regulation of P-450scc gene expression during functional maturation of the prepubertal ovary.

Endogenous digoxin-like factor contributes to the elevation of systemic resistance in rats exposed to high salt intake from prepuberty

The acute administration of anti-digoxin serum (ADS) caused a pronounced blood pressure decrease only in those hypertensive rats that were treated with desoxycorticosterone acetate (DOCA) and 1% saline from prepuberty. This was due to a rapid decrease in systemic resistance which was partially compensated by increased cardiac output. There were no similar effects of ADS in rats treated in the same manner in adulthood only. Different mechanisms might be responsible for blood pressure elevation induced by high salt intake in youth or in adulthood. The participation of endogenous digoxin-like factor in the maintenance of elevated systemic resistance in DOCA-salt hypertensive rats is a typical case.

Effects of anterior hypothalamic lesions on the sexual behavior of prenatally-stressed male rats

Sprague-Dawley females were exposed to the stress of heat, restraint and bright lights during the third trimester of gestation. Virtually all male offspring tested for masculine sexual behavior as adults ejaculated and copulated with lure females. Also prenatally-stressed males exhibited two to three times as many lordotic responses as did males from nonstressed mothers. Because animals were crossfostered, an in utero action of prenatal stress is supported. Anterior hypothalamic (AHA) lesions significantly reduced the number of lordotic responses observed in prenatally-stressed male rats compared to those observed in prenatally-stressed males bearing sham lesions of the AHA. The possibility is presented that prenatal stress may influence the developing male brain.

Fine structural changes in uterine smooth muscle and fibroblasts in response to estrogen

The fine structure of the estrogen-primed uterus was examined in two series of rats, with emphasis upon the alterations in smooth muscle cells and fibroblasts. The first series of animals were mature animals that were sacrificed at diestrus or estrus. The second series consisted of prepubertal rats (57-70 g) that received subcutaneous injections of estradiol-17 beta in 20% alcohol. Four groups of animals received the hormone twice daily for 3 days for a total dose of 0.06, 0.6, 6.0, or 60.0 microg, respectively. An estrogenic response was observed in all groups as indicated by an increase in uterine weight. Control groups consisted of either untreated animals or animals receiving 20% alcohol. All animals were sacrificed on the 4th day. The fibroblasts and smooth muscle cells in the controls were similar to their counterparts in the mature animal in diestrus. They were small, contained relatively little rough endoplasmic reticulum, and the connective tissue cells appeared like fibrocytes. All of the estrogen-treated animals were similar in appearance and were comparable to their counterparts in the mature animal in estrus. Both the smooth muscle cells and the fibroblasts were increased in size, demonstrated a marked enlargement and dilation of ergastoplasmic cisternae, and contained increased numbers of attached and free cytoplasmic ribosomes. The presence of an extensive rough endoplasmic reticulum in the smooth muscle cells of the stimulated uterus is in marked contrast to the appearance of these cells in other tissues. These observations correlate with previous biochemical studies by other workers, in which estrogens have been shown to promote the synthesis of uterine RNA, collagen, and noncollagenous protein, and suggest that smooth muscle cells may participate in the synthesis of connective tissue proteins.