Prepubertal treatment with estrogen or testosterone precipitates the loss of regular estrous cyclicity and normal gonadotropin secretion in adult female rats

To examine the effects of prepubertal steroid environment on subsequent estrous cyclicity and gonadotropin secretion, Silastic implants containing 25, 50 or 100% 17 beta-estradiol (E2;n=34), 50% diethylstilbestrol (DES; n=16) or 50% testosterone (T; n=17) were placed into female rats at 12 days of age and removed on the day of vaginal opening (18-24 days of age). At 80 days of age, the percentages of regularly cycling females in the E2-(three groups combined), DES- and T-implanted groups were 59%, 0% and 59%, respectively. By 110 days of age, the percentages were reduced to 24%, 0% and 0%, and at 140 days of age 6%, 0% and 0%, respectively. Many of these females displayed irregular estrous cycles followed by a persistent estrous (PE) state. By contrast, 89% of the control females (blank implants or no implant) maintained regular cycles up to 140 days of age. At 150 days of age, an i.p. injection of gonadotropin-releasing hormone (GnRH; 100 ng/100 g BW) markedly increased serum luteinizing hormone (LH), but not follicle-stimulating hormone (FSH), in intact PE females treated prepubertally with E2 implants. After the test with GnRH, PE rats were ovariectomized (OVX). Thirty days after OVX, similar GnRH administration significantly increased serum levels of both LH and FSH, but these responses were significantly (P less than 0.01) reduced when compared with those in OVX controls. Progesterone administration to estradiol benzoate-primed, acutely (3 days) OVX, or long-term (43 days) OVX-PE females did not increase LH or FSH release. These results indicate that exposure to exogenous estrogen or T prior to puberty precipitates the decline in estrous cyclicity associated with the loss of gonadotropin surge response, presumably due to an alteration in hypothalamic GnRH release.     

Escherichia coli gal K和gpt基因注入小鼠受精卵的研究

含有E.coli galK和gpt基因的重组DNA pPB22用显微注射法导入昆明白小鼠受精卵,经发育,最后得到21只成年小鼠。其中1只小鼠的肝脏显示出E.coli gpt酶活性,但未检测出E.coli galK酶活性。印迹分子杂交表明,外源的pPB 22重组DNA已整合到2只小鼠的染色体上,其中包括那只肝脏中显示E.coli gpt酶活性的小鼠。     

Beta-adrenergic stimulation evokes a rapid, Ca2+-dependent stimulation of endocytosis, hexose and amino acid transport associated with increased Ca2+ fluxes in mouse kidney cortex

The beta-adrenergic agonist 1-isoproterenol evokes an acute (less than 5 min) stimulation of endocytosis, hexose transport and amino acid transport, measured by the temperature-sensitive uptake of HRP, 3H-DG and 14C-AIB, in mouse kidney cortex slices. This stimulation is concentration dependent and is maximal at 10(-8)-10(-7) M isoproterenol. Peroxidase cytochemistry showed that the hormonal increase in HRP uptake is confined to proximal tubules. The rapid membrane response is abolished in a calcium-free medium and by the beta-adrenergic antagonist propranolol, indicating Ca2+- and beta-adrenoreceptor-dependence. Isoproterenol (1 microM) rapidly (less than 30 sec) stimulates the influx and efflux of 45Ca in cortex slices. Isoproterenol also decreased mitochondrial 45Ca and increased soluble 45Ca. These results indicate that beta-adrenergic stimulation of membrane transport functions involves an increased influx of extracellular calcium and a mobilization of intracellular (mitochondrial) calcium. An increase in cytosolic Ca2+ concentration appears to be the regulatory signal for these membrane transport processes.     

Temperature control of initiation of protein synthesis in Escherichia coli

When an exponentially growing culture of Escherichia coli is cooled to below 8 °C, initiation of protein synthesis appears to be blocked, while the elongation of initiated proteins continues until they are completed. This is demonstrated here by showing that nascent polypeptide chains increase in size during a 5 °C incubation and that f2 viral coat protein is completed, but not initiated. Upon rewarming, the cells initiate protein synthesis synchronously. This is demonstrated by a transient rise in the incorporation of methionine which is used to initiate protein synthesis.     

Genetic Recombination in Coprinus. IV. a Kinetic Study of the Temperature Effect on Recombination Frequency

At the restrictive conditions (35 degrees under continuous light) Coprinus lagopus is unable to initiate premeiotic S phase which takes place normally within 8-10 h of karyogamy. A shift-up to the restrictive conditions causes an arrest of the basidiocarps at this critical stage. A prolonged arrest causes a reversal to mitosis (Lu 1974b). Incubation of basidiocarps at the restrictive conditions before this critical stage causes no increase in recombination frequency (R.F.) in the loci studied. An arrest of 4 h at the critical stage still causes no R.F. increase, but 12-13 h and 18-19 h arrests cause increases of 50% and 90% over the controls, respectively. Thus R.F. can be increased even before the cells are fully committed to meiosis.-A 3-h heat treatment at the beginning of S phase (or 8 h before karyogamy) also causes some (30%) increase in R.F. while the same treatment at late S phase (or 3 h before karyogamy) causes a substantial (164%) increase in R.F. over the controls. A 3-h heat treatment before S phase causes no increase in R.F.-Pachytene is also responsive to temperature treatments (Lu 1969). The maximum R.f. increase is 100% by heat and 220% by cold treatment. The shortest time that can cause the maximum increase in recombination by high temperature is 3 h and that by cold treatment is 7 h. These durations are correlated with the length of the pachytene stage under the treatment conditions. The kinetic data show that the increase in R.F. caused by high and low temperatures follows two-hit kinetics and their rate of increase is almost identical. The higher increase in R.F. by low temperature can be attributed to the increased duration of pachytene and therefore R.F. is a function of time. The longer the homologous chromosomes are held together, the higher the recombination frequency.