Luteinizing hormone and growth hormone secretion in ewes infused intracerebroventricularly with neuropeptide Y.

Neuropeptide Y (NPY) provides an important hypothalamic link between nutritional status and neuroendocrine mechanisms regulating growth and reproduction. The objective of the following series of experiments was to determine the effects of single or continuous administration of NPY on secretion of luteinizing hormone (LH) and (or) growth hormone (GH). In experiment 1, four ovariectomized (OVX) ewes and four OVX + estrogen-treated ewes each received, in a 4 x 4 Latin Square arrangement of treatments, a single injection of 0, 0.5, 5, or 50 microg NPY via an intracerebroventricular (i.c.v.) cannulae to determine the effects on secretion of GH. NPY significantly elevated serum GH at the 50 microg dose regardless of estrogen exposure (P = 0.003). In experiment 2, eight OVX ewes were infused i.c.v. with NPY or saline (n = 4/trmt) continuously for 20 h in a linearly increasing dose, ending at 50 microg/h NPY. Blood samples were collected via jugular cannulae every 10 min during hour -4-0 (interval 1, pre-treatment), hour 6-10 (interval 2) and hour 16-20 (interval 3) relative to the initiation of infusion (0 h). Mean LH and LH pulse frequency were lower in NPY- versus saline-infused ewes during intervals 2 and 3 (P < 0.01), but NPY had no discernable effect on serum GH (P > 0.10). In experiment 3, four OVX ewes were continuously infused with NPY as in experiment 2, except that the maximum 50 microg/h dose was achieved after only 10 h of infusion. Blood samples were collected every 10 min, beginning 4 h before and continuing until 4h after the NPY infusion. Mean serum LH changed significantly over time (P = 0.0001), decreasing below pre-treatment levels by hour 3 of NPY infusion (P < 0.01), and returning to pre-treatment concentrations following the end of infusion (P > 0.15). Serum GH also changed significantly over time (P < 0.001). Mean GH levels tended to be greater than pre-treatment levels by hour 2 of infusion (P < 0.08), but thereafter returned to basal levels. Serum GH also increased following the end of NPY infusion (P < 0.03). From these data we conclude that NPY exerts a persistent inhibitory effect on secretion of LH, and may stimulate the secretion of GH during the initiation and cessation of infusion of NPY. These observations support a role for NPY in mediating the effects of undernutrition on both LH and GH, and also provide evidence for potential mechanisms by which leptin, acting through NPY, may stimulate the secretion of GH.

Reproductive endocrinology and toxicological pathology over the life span of the female rodent.

Understanding the pathology of the female reproductive system with respect to toxicology requires a basic understanding of morphology and function of the system over time because the nature of the female reproductive system is cyclical. Thus, the morphology and the endocrinology is dependent on age and time, as form follows function and function follows form. The life span of the rodent is used as an outline to present an overview of key morphological and endocrinological events important for toxicologic pathologists to consider in study evaluations. Environmental and pharmaceutical compounds differentially impact the organs individually and/or the system in its entirety in a time- and dose-dependent way. Examples are used to illustrate the consequences of exposures at different times and with different outcomes.

Alterations in insulin-like growth factor-1 gene and protein expression and type 1 insulin-like growth factor receptors in the brains of ageing rats.

Ageing in mammals is characterized by a decline in plasma levels of insulin-like growth factor-1 that appears to contribute to both structural and functional changes in a number of tissues. Although insulin-like growth factor-1 has been shown to provide trophic support for neurons and administration of insulin-like growth factor-1 to ageing animals reverses some aspects of brain ageing, age-related changes in insulin-like growth factor-1 or type 1 insulin-like growth factor receptors in brain have not been well documented. In this series of studies, insulin-like growth factor-1 messenger RNA and protein concentrations, and type 1 insulin-like growth factor receptor levels were analysed in young (three to four- and 10-12-month-old), middle-aged (19-20-month-old) and old (29-32-month-old) Fisher 344 x Brown Norway rats. Localization of insulin-like growth factor-1 messenger RNA throughout the lifespan revealed that expression was greatest in arteries, arterioles, and arteriolar anastomoses with greater than 80% of these vessels producing insulin-like growth factor-1 messenger RNA. High levels of expression were also noted in the meninges. No age-related changes were detected by either in situ hybridization or quantitative dot blot analysis of cortical tissue. However, analysis of insulin-like growth factor-1 protein levels in cortex analysed after saline perfusion indicated a 36.5% decrease between 11 and 32 months-of-age (P<0.05). Similarly, analysis of type 1 insulin-like growth factor receptor messenger RNA revealed no changes with age but levels of type 1 insulin-like growth factor receptors indicated a substantial decrease with age (31% in hippocampus and 20.8 and 27.3% in cortical layers II/III and V/VI, respectively). Our results indicate that (i) vasculature and meninges are an important source of insulin-like growth factor-1 for the brain and that expression continues throughout life, (ii) there are no changes in insulin-like growth factor-1 gene expression with age but insulin-like growth factor-1 protein levels decrease suggesting that translational deficiencies or deficits in the transport of insulin-like growth factor-1 through the blood-brain barrier contribute to the decline in brain insulin-like growth factor-1 with age, and (iii) type 1 insulin-like growth factor receptor messenger RNA is unchanged with age but type 1 insulin-like growth factor receptors decrease in several brain regions. We conclude that significant perturbations occur in the insulin-like growth factor-1 axis with age. Since other studies suggest that i.c.v. administration of insulin-like growth factor-1 reverses functional and cognitive deficiencies with age, alterations within the insulin-like growth factor-1 axis may be an important contributing factor in brain ageing.

Effects of lifelong moderate caloric restriction on levels of neuropeptide Y, proopiomelanocortin, and galanin mRNA.

We are interested in how neuropeptides that regulate both food intake and reproductive function change with age and how life-prolonging moderate caloric restriction may influence the expression of these neuropeptides. We measured neuropeptide Y (NPY) and proopiomelanocortin (POMC) mRNA in the arcuate nucleus (AN), and galanin (GAL) mRNA in the AN, paraventricular nucleus (PVN) and medial septum-diagonal band of Broca in young, middle-aged and old female rats on a controlled feeding regimen. Female Sprague-Dawley rats (7 weeks old) were placed on caloric restriction (CR; n = 70) which was 60% of ad libitum (AL) intake measured in control rats (n = 70). Rats were rapidly decapitated 2.5 weeks following ovariectomy, when they were 4, 12, or 18 months old. Brains were frozen and coronal sections (12 microns) were cut at -20 degrees C using a cryostat. Relative levels of NPY, POMC and GAL mRNA were measured using in situ hybridization histochemistry. cDNA clones complementary to rat NPY, mouse POMC and rat GAL were used to synthesize 35S-UTP-labeled cRNA probes. Slides were dipped in photographic emulsion. Silver grains were quantified using computer-assisted image analysis. Caloric restriction increased NPY mRNA/cell, decreased POMC mRNA/cell in the AN, and did not influence GAL mRNA/cell. Age and caloric restriction did not influence the number of cells with detectable NPY mRNA, POMC mRNA or GAL mRNA. Reproductive status at the time of decapitation influenced both the level and the number of cells expressing GAL mRNA in the PVN. In summary, CR differentially affects levels of NPY, POMC and GAL mRNA in the AN. In this animal model, there was no statistically significant effect of age nor any interaction between age and diet on expression of any of these genes between 4 and 18 months of age.

Distribution and levels of insulin-like growth factor I mRNA across the life span in the Brown Norway x Fischer 344 rat brain.

Previous studies have reported changes in insulin-like growth factor I (IGF-I) mRNA expression during early postnatal development of the rat brain. Although changes in IGF-I gene expression have been documented in a wide range of central nervous system structures during early development and investigated in the hippocampus during aging, no study has compared changes in IGF-I gene expression in different brain regions across the life span. The present study assessed the distribution of IGF-I gene expression using in situ hybridization in rats aged 2-30 months. Dot blots were used as a quantitative assessment of cortical IGF-I mRNA. Results indicate that both the distribution and levels of brain IGF-I mRNA do not change significantly between 2 and 30 months of age in the rat. However, in spite of relatively constant levels of mRNA, other studies from our laboratory have demonstrated that cortical IGF-I protein levels decrease 36.6% between 11 and 32 months of age, suggesting that IGF-I function is decreased with increasing age.

Aging of the female reproductive system: a window into brain aging.

The menopause marks the permanent end of fertility in women. It was once thought that the exhaustion of ovarian follicles was the single, most important explanation for the transition to the menopause. Over the past decade, this perception has gradually changed with the realization that there are multiple pacemakers of reproductive senescence. We will present evidence that lends credence to the hypothesis that the central nervous system is a critical pacemaker of reproductive aging and that changes at this level contribute to the timing of the menopause. Studies demonstrate that an increasing de-synchronization of the temporal order of neuroendocrine signals may contribute to the accelerated rate of follicular loss that occurs during middle age. We suggest that the dampening and destabilization of the precisely orchestrated ultradian, circadian, and infradian neural signals lead to miscommunication between the brain and the pituitary-ovarian axis. This constellation of hypothalamic-pituitary-ovarian events leads to the inexorable decline of regular cyclicity and heralds menopausal transition.

Dynamic changes in gonadotropin releasing hormone receptor mRNA content in the mediobasal hypothalamus during the rat estrous cycle.

The purpose of the present study was to determine if GnRH receptor mRNA levels in the rat brain undergo changes during the estrous cycle. We focused on the arcuate and ventromedial nuclei of the hypothalamus and on the hippocampus which are sites in the rat central nervous system that have been shown to contain measurable amounts of GnRH receptor mRNA. Groups of regularly cycling female rats were decapitated at 08.00 and 17.00 h of each day of the estrous cycle, trunk blood was collected for radioimmunoassay analysis of circulating LH levels, and the brains were processed for 'in situ' hybridization. A cDNA probe encoding the rat pituitary GnRH receptor was transcribed 'in vitro' in the presence of (33)P-alpha UTP and used under saturating conditions to label GnRH receptor mRNA. The results show that in the arcuate and ventromedial nuclei GnRH receptor mRNA levels are relatively high during diestrus 1, they decline slightly during diestrus 2 before they rise to the highest levels at 08.00 h of proestrus. By 17.00 h of proestrus, GnRH receptor mRNA levels had declined to the lowest levels of the estrous cycle where they remain through the morning of estrus. The GnRH receptor mRNA levels rise again sharply during the afternoon of estrus. The changes in the hippocampus follow a similar pattern in that a decline in GnRH receptor mRNA levels to its lowest levels occurs between 08.00 and 17.00 h of proestrus. However, the changes in the hippocampus did not reach statistical significance. It is concluded that GnRH receptor mRNA levels in the arcuate and ventromedial nuclei are upregulated in the morning of proestrus, probably by rising estradiol levels, in preparation for the GnRH-LH preovulatory surge while this effect of estradiol is not apparent in the hippocampus.

Life-long moderate caloric restriction prolongs reproductive life span in rats without interrupting estrous cyclicity: effects on the gonadotropin-releasing hormone/luteinizing hormone axis.

Restricting food intake to 60% that of ad libitum-fed rats results in an extended life span, reduced incidence of age-related diseases, and delayed reproductive senescence. We used this animal model to further elucidate the mechanisms whereby reproductive senescence is delayed. Female Sprague-Dawley rats (7 wk old) were calorically restricted (CR; n = 70) to 60% of the ad libitum(AL) intake measured in control rats (n = 70). Rats were individually housed under a 14L:10D cycle and fed daily within 1.5 h of lights-off. Body weights were monitored every 2 wk, and vaginal lavage was performed until rats were ovariectomized (OVX). Two weeks after OVX, when rats were 4, 12, or 18 mo of age, blood samples were taken via jugular cannulae every 6 min for 3 h, and the plasma was assayed for rat LH. The resulting profiles were examined through use of Cluster analysis for mean LH concentrations, LH pulse amplitude, and interval between LH pulses. CR rats grew at a slower rate, and then maintained body weights at approximately 76% that of AL controls between 4 and 17.5 mo of age. The onset of persistent estrus was delayed by 4 mo in CR rats. Average cycle length was longer (p < 0.01) by less than 0.5 days in CR compared with AL rats between 3.5 and 5.5 mo of age but not different between 6.5 and 11.5 mo. Mean levels of LH in OVX rats decreased with age (p < 0.01), increased with caloric restriction (p < 0.05), and decreased with declining cycling status of the animal prior to OVX (regular [reg] vs. irregular [ir] vs. persistent estrus [pe]; p < 0.05). The increased mean LH due to caloric restriction was attributed to an increase in mean pulse amplitude and not to a decrease in time interval between LH pulses. From these data we conclude that the beneficial effects of caloric restriction on reproductive longevity may be acting at the level of the hypothalamus and/or pituitary to enhance LH secretion and do not require a delay in puberty or a period of acyclicity.

Neuropeptide-Y neurons projectioning to the medial septum-diagonal band do not have access to fenestrated capillaries in the rat brain.

The aims of this study were to (1) determine the localization of neuropeptide-Y (NPY)-containing perikarya which project to the medial septum-diagonal band (MSDB), a brain region rich in gonadotropin-releasing hormone (GnRH) producing perikarya, and (2) determine if NPY neurons have access to fenestrated capillaries as well. Fluorescent retrograde tracing after microinjection of fluororuby (FR) into the MSDB, and peripheral injection of fluorogold (FG), was used in combination with immunofluorescence for NPY. Injection of FR into the MSDB resulted in retrograde labeling of neurons in the hypothalamic arcuate nucleus (ARC) and brainstem noradrenergic cell groups A1 and A2, as well as other regions. The largest populations of NPY neurons were located in the ventromedial ARC and several of these perikarya contained FR indicating that they project to the MSDB. Defined cell groups in the areas A1 and A2 of the brainstem also contained large numbers of NPY neuron perikarya, and several of these contained FR. In addition, we observed isolated incidences of FR-labeled NPY perikarya in the amygdala and hippocampus. A small population of NPY neurons in the ARC contained FG, indicating that they are in contact with fenestrated capillaries and hence are neuroendocrine cells; however, none of these neurons contained FR. We suggest that NPY neurons in the ARC modulate GnRH function via innervation of the MSDB and LH release via release into fenestrated capillaries of the hypophysial-portal system.

Neuroendocrine concomitants of reproductive aging.

Depletion of ovarian follicles is often thought to be the determining factor in female reproductive aging. However, increasing evidence suggests that neural and neuroendocrine changes play important causative roles in the decline of regular reproductive cycles leading to the menopause. A blunting or suppression in the daily pattern of secretion of several neuroendocrine hormones has been documented in aging laboratory animals and humans. Investigators have designed experiments to test whether these changes reflect multiple unrelated changes in the regulation of each of these hormones, or whether these alterations result from a fundamental change in the time-keeping mechanism that underlie these patterns of hormone secretion. Oscillations that occur approximately every 24 h are a hallmark of most living organisms. These cycles provide the organism with the capability of coordinating events that occur at higher (hourly) and lower (weekly or monthly) frequencies within an individual organism, and with the capability of synchronizing these events with the external environment. In mammals, the hypothalamic suprachiasmatic nucleus is thought to be a master oscillator that regulates most circadian rhythms in mammals. Perturbations in temporal organization occur during aging and influence multiple physiological systems, including reproductive cyclicity in females. Thus, the question for neuroendocrinologists is: Do changes in the cyclic pattern of hormone secretion reflect a change in the master oscillator, and do these changes play a role in female reproductive aging? Data from our laboratory demonstrate that the timing of the preovulatory and steroid-induced luteinizing hormone (LH) surge changes during middle-age in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of food restriction on neuropeptide-Y, proopiomelanocortin, and luteinizing hormone-releasing hormone gene expression in sheep hypothalami.

Chronic food restriction decreases secretion of LH as a result of inhibitory influences on secretion of LHRH. We have previously reported that neuropeptide-Y (NPY) may directly or indirectly mediate this inhibitory effect on LHRH secretion. In the study reported here, we tested the hypothesis that long-term food restriction suppresses tonic release of LH as a result of 1) an increase in biosynthetic activity of NPY neurons in the arcuate nucleus of the hypothalamus, 2) an increase in activity of neurons that secrete beta-endorphin, and 3) a decrease in biosynthesis of LHRH. To test predictions of the hypothesis, we compared levels of mRNA encoding NPY, proopiomelanocortin (POMC; the precursor peptide of beta-endorphin), and LHRH, as well as tonic secretion of LH in food-restricted and well-nourished ewe lambs. Ten ewe lambs were ovariectomized at 18 wk of age and randomly assigned to receive either 100% nutritional requirements (FED; n = 5), or 30% requirements (R; n = 5) between 18 and 25 wk of age. At 25 wk of age, blood samples were taken every 10 min for 6 h and assayed for LH. The tonic release of LH in R lambs was less than that of FED lambs. Hypothalami were collected 4 days after blood sampling and sectioned at 12 microns for use in in situ hybridization. Radiolabeled molecular probes specific for mRNAs encoding NPY, POMC, or LHRH were hybridized to hypothalamic tissue sections. Levels of NPY mRNA were 88% greater in R vs. FED lambs (p < 0.01), whereas levels of POMC mRNA were 52% lower in R vs. FED lambs (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Central actions of neuropeptide-Y may provide a neuromodulatory link between nutrition and reproduction.

Central injection of neuropeptide-Y (NPY) has been shown to attenuate secretion of LH in ovariectomized rats, rabbits, and monkeys. Several investigators have reported elevated concentrations of NPY in the central nervous system of undernourished animals. The relationship between nutrition and reproduction positions NPY as a potential neuromodulator involved in nutritionally induced changes in secretion of LH. Three experiments were conducted with the following objectives: 1) to examine the effects of NPY on secretion of LH in ovariectomized (OVX) ewes and the influence of estradiol-17 beta (E) on these effects; 2) to determine whether NPY may act through direct effects on the pituitary to influence secretion of LH; and 3) to determine changes in concentrations of NPY in laterocerebro-spinal fluid (CSF) of food-restricted ewes compared to well-fed ewes. In Experiment 1, OVX ewes with s.c. implants of E (OVX + E, n = 4) or no steroid treatment (OVX, n = 4) were fitted with intracerebroventricular (i.c.v.) and jugular cannulae. One of 4 doses of porcine NPY (pNPY; 0, 0.5, 5, or 50 micrograms) was injected i.c.v. and blood samples were collected every 10 min for 4 h prior to and following i.c.v. injection. Blood serum was assayed for LH. The experiment was replicated four times such that each ewe received each dose of pNPY. Mean concentrations of LH as well as frequency and amplitude of pulses of LH were attenuated in response to i.c.v. injection of pNPY in a dose-related manner in both OVX and OVX + E ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of interferon-gamma on complement gene expression in different cell types.

We have studied the expression of the complement components C2, C3, factor B, C1 inhibitor (C1-inh), C4-binding protein (C4-bp) and factor H in human peripheral blood monocytes, skin fibroblasts, umbilical vein endothelial cells (HUVEC) and the human hepatoma cell line G2 (Hep G2) in the absence and the presence of interferon-gamma (IFN-gamma). E.l.i.s.a. performed on culture fluids, run-on transcription assays, Northern blot and double-dilution dot-blot techniques confirmed that monocytes expressed all six components, whereas fibroblasts, HUVEC and HepG2 each expressed five of the six components. Fibroblasts and HUVEC did not synthesize C4-bp, and Hep G2 did not produce factor H. In addition to these differences, the synthesis rates of C3, C1-inh and factor H were not the same in all cell types. However, the synthesis rates of C2 and factor B were similar in all four cell types. The half-lives of the mRNAs were shorter in monocytes than in other cell types. Monocyte factor H mRNA had a half-life of 12 min in monocytes, compared with over 3 h in fibroblasts and HUVEC. The instability of factor H mRNA in monocytes may contribute to their low factor H secretion rate. IFN-gamma produced dose-dependent stimulation of C2, factor B, C1-inh, C4-bp and factor H synthesis by all cell types expressing these proteins, but decreased C3 synthesis in all four cell types. Cell-specific differences in the response to IFN-gamma were observed. The increased rates of transcription of the C1-inh and factor H genes in HUVEC were greater than in other cell types, while the increased rate of transcription of the C2, factor B and C1-inh genes in Hep G2 cells was less than in other cell types. IFN-gamma did not affect the stability of C3, factor H or C4 bp mRNAs, but increased the stability of factor B and C1-inh mRNAs and decreased the stability of C2 mRNA. Although these changes occurred in all four cell types studied, the half-life of C1-inh mRNA in monocytes was increased almost 4-fold, whereas the increases in the other cell types were less than 30%. These data show that the constitutive synthesis rates of complement components may vary in the different cell types. They also show that the degree of change in synthesis rates in response to IFN-gamma in each of the cell types often varies due to differences in transcriptional response, sometimes in association with changes in mRNA stability.

Effects of dietary energy on ovarian function, estrogen suppression of luteinizing hormone and follicle-stimulating hormone, and competency of the gonadotropin surge.

Fall-born ewe lambs were utilized to test the hypotheses that 1) inhibitory effects of increasing day length supersedes the stimulatory effects of increased nutrient intake on secretion of LH; 2) chronic undernutrition impairs ovarian function independent of changes in secretion of LH; and 3) undernutrition alters hypothalamic-pituitary responsiveness so as to influence feedback effects of estradiol on secretion of gonadotropins. Lambs were fed a low-energy diet (LE) from 14 to 26 wk of age to maintain a body weight of 24 kg during an inhibitory photoperiod. At 26 wk of age (experiment 1), lambs were either switched to a high-energy diet (HE; n = 10) or maintained on LE (n = 10). During increased nutrient intake, the frequency of pulses of LH remained at prepubertal levels, indicating that the inhibitory effects of photoperiod on tonic secretion of LH prevent the stimulatory effects of increased nutrition in chronically undernourished lambs. In experiment 2, lambs (33 wk of age) received hourly injections of ovine LH (15 micrograms; n = 6/diet group) or saline (n = 4/diet group) for 60 h during an inhibitory photoperiod. Chronically undernourished lambs were able to secrete estradiol, elicit a surge of LH, and form luteal tissue in the same manner as well-nourished lambs. After experiment 2, 4 lambs in each diet group were either bilaterally ovariectomized (OVX) or sham operated (INT) for experiment 3. At 36 wk of age, lambs were infused with estradiol-17 beta at a linearly increasing rate of 0.08 pg/ml for 56 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of recombinant DNA-derived somatotropin and dietary energy intake on development of beef heifers: II. Concentrations of hormones and metabolites in blood sera.

The effects of somatotropin (STH) and energy intake on serum concentrations of glucose (GLU), insulin (INS), nonesterified fatty acids (NEFA), urea nitrogen (UN) and insulin-like growth factor-I (IGF-I) were determined in 40 Angus heifers. At 7 mo (208 +/- 8 d) of age heifers were assigned to four treatment groups: 1) vehicle (V) + high energy (HE; 2.68 Mcal ME/kg DM), 2) recombinant DNA-derived STH (20.6 mg/d; s.c.) + HE, 3) V + low energy (LE; 2.22 Mcal ME/kg DM) or 4) STH + LE. Animals remained on treatments until an average of 15.5 mo of age. Blood samples were taken every 30 min for 4 h at 9, 11, 13 and 15 mo of age to determine circulating concentrations of metabolites and hormones. Serum IGF-I was increased (P less than .01) by STH injections, but this effect appeared to diminish with age (STH x age; P less than .01). Energy intake did not influence IGF-I levels. Somatotropin increased (P less than .01) serum GLU in heifers fed the HE diet but only tended (P = .08) to increase GLU in those fed the LE diet (STH x energy; P = .05). Although STH increased (P less than .01) serum INS in both energy groups, the response in heifers fed the HE diet was greater (P less than .02) than that in heifers fed the LE diet (STH x energy; P less than .05). Heifers fed LE had higher (P less than .01) concentrations of NEFA than heifers fed HE.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of recombinant DNA-derived somatotropin and dietary energy intake on development of beef heifers: I. Growth and puberty.

The effects of dietary energy intake and somatotropin (STH) on growth and puberty were studied in 40 Angus heifers. At an average age of 7 mo (208 +/- 8 d), heifers were assigned to four treatment groups: 1) vehicle (V) + high energy (HE; 2.68 Mcal ME/kg DM), 2) recombinant DNA-derived STH (20.6 mg/d; s.c.) + HE, 3) V + low energy (LE; 2.22 Mcal ME/kg DM) or 4) STH + LE. Animals remained on treatments until 15.5 mo of age. Body weights (BW), hip heights (HH) and areas of pelvic openings (PA) were measured every 28 d and backfat thicknesses (BF) were measured every 56 d. Plasma progesterone was measured in blood samples taken three times per week beginning at 9 mo of age to determine age at first ovulation. Heifers fed HE were heavier (P less than .01), gained faster (P less than .01) and had greater BF (P less than .01) than those fed LE. Animals treated with STH gained faster (P less than .01) and were heavier (P less than .05) between 12 and 15 mo of age than V-treated heifers. Heifers treated with STH also had less BF (P less than .05) and a tendency for a greater (P = .08) increase in HH than in V-treated heifers. Somatotropin interacted with energy (P less than .05) and age (P less than .01) to influence PA. Somatotropin increased (P less than .01) PA in heifers fed the HE diet but not in those fed the LE diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of feeding tall fescue seed infected with endophytic fungus (Acremonium coenophialium) on the estrous cycle in CD-1 mice.

The objective of this study was to assess the effects of endophyte-infected tall fescue (G1-307) seed (80% infected, by Acremonium coenophialum) on the estrous cycle in CD-1 mice. Twelve 60-day-old CD-1 female mice were randomly allocated to one of two dietary treatments containing 50% laboratory chow and (1) 50% endophyte-free (noninfected) fescue seed; (2) 50% endophyte-infected fescue seed. All mice were fed ad libitum. On day 35 of the study all mice were allowed access to a diet containing 100% laboratory chow for 7 days. Vaginal smears of each female were prepared daily throughout the 42 day trial period. All vaginal smears were stained and evaluated to determine phase of the estrous cycle. The days (+/- SE) to the first abnormal occurrence in the estrous cycle for treatments one and two were 27.0 +/- 5.6 and 16.7 +/- 5.2, respectively. The percent abnormal cycles of the total cycles observed between treatments one and two were 20.5 +/- 6.1 and 39.3 +/- 12.5, respectively. Mice on treatment two exhibited a greater frequency of abnormal sequences of the phases of the estrous cycle and greater cycle length (P less than 0.05). The results suggest that the infected fescue seed had a significant effect on the estrous cycle of the mouse (P less than 0.05).

Recombinant plasmids containing Xenopus laevis globin structural genes derived from complementary DNA.

Details are presented of the in vitro synthesis of double-stranded DNA complementary to purified Xenopus globin messenger RNA, using a combination of reverse transcriptase, fragment 'A' of E. coli DNA polymerase 1 and S1 endonuclease. After selection of duplex DNA molecules approaching the length of Xenopus globin messenger RNA by sedimentation of the DNA through neutral sucrose gradients, the 3'-OH termini of the synthetic globin gene sequences were extended with short tracts of oligo dGMP using terminal transferase. This material was integrated into oligo dCMP-extended linear pCR1 plasmid DNA and amplified by transfection of E. coli. Plasmids carrying globin sequences were identified by hybridization of 32P-labelled globin mRNA to total cellular DNA in situ, by hybridization of purified plasmids to globin cDNA in solution, by analysis of recombinant DNA on polyacrylamide and agarose gels, and by heteroduplex mapping. The results show that extensive DNA copies of Xenopus globin mRNA have been integrated into recombinant plasmids.