The current experiment was conducted with beef cows during the first 2 weeks postpartum (PP) to determine the effects of suckling and low-level increases of systemic progesterone on secretory characteristics of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in peripheral plasma. Variables measured included mean gonadotropin concentrations, FSH/LH pulse frequencies, pulse amplitudes and synchrony of coincident release. Suckled (S) cows had lower (P less than 0.01-P less than 0.05) mean concentrations of FSH and LH in plasma, lower (P less than .05) FSH and LH pulse frequencies and a lower (P less than 0.05) pulse synchrony (21.6 vs 72.3% coincident pulses) than nonsuckled (NS) cows on Day 7 PP. Neither FSH nor LH pulse amplitude was affected by suckling. Similar differences existed for mean gonadotropin concentrations, pulse frequencies and pulse synchrony on Day 14 PP between S and NS cows. Implanting cows with progesterone implants on Day 7 PP, which chronically increased plasma progesterone to 0.5-0.6 ng/ml, increased (P less than 0.05) mean plasma FSH and LH concentrations, FSH and LH pulse frequencies and pulse synchrony (87.5 vs. 66.3%) in NS-implanted (NSI) versus NS-nonimplanted (NSNI) cows. Progesterone implants had no beneficial effect in S cows. Thus, three major findings seem pertinent: 1) associated with the suckling-induced depression of episodic gonadotropin release was a marked decline in FSH/LH pulse synchrony; 2) a high degree of FSH/LH pulse synchrony (72-88%) was restored in the absence of suckling when gonadotropin pulse frequency increased to 4-5/6 h; 3) the absence of suckling, followed by the provision of low-level progesterone stimulation for 7 days, appeared to have additive effects on FSH and LH secretion. These results provide evidence that the neuroendocrine block associated with suckling in early PP beef cows is, in addition to being associated with depressed LH release, comprised of characteristic anomalies in FSH secretion, FSH/LH pulse synchrony and failure to respond to a putative hypothalamo-hypophyseal potentiator, progesterone.
A simple bioassay was developed to determine insecticidal fumigancy of natural constituents of insect exocrine secretions and commercially available fumigants against adults of Drosophzla melanogaster. It was useful to estimate 50 %-mortality times of the flies below and at saturation concentrations of the test compounds. In the bioassay natural products like short chain alcohols (I-pentanol, 1-octanol), aromatic compounds (benzaldehyde, benzonitrile, acetophenone), a ketone (3-methyl-2-heptanone), acids (2-methyl-butanoic acid) or spiroacetals (2-methyl-l,7-dioxaspiro [5.5] undecane) exhibited a drastic insecticidal fumigancy at extraordinary low vapor concentrations as compared to commercial fumigants. At least the highly active natural compound actinidin shows a similar high vapor concentration as compared to the synthetic fumigants. The biological significance especially of the low volatile gland constituents is discussed.
Gsp oncogenes are present in about 40% of somatotropinomas. They result in excessive cAMP production and have been proposed to be the cause of increased GH secretion. We have used in vitro cell culture to compare the biochemical characteristics of somatotropinomas with and without gsp oncogenes (gsp-positive and gsp-negative tumors, respectively). Of 30 somatotropinomas examined, 10 proved to be gsp positive, as determined by sequence analysis of DNA generated by the polymerase chain reaction. The somatostatin analog, octreotide, powerfully inhibited GH secretion by gsp-positive somatotropinomas, but had no effect on 8 of 13 gsp-negative tumors. Five of 20 gsp-negative and 4 of 10 gsp-positive tumors failed to respond to GHRH, whereas stimulatory effects ranging from 37-500% increases in GH secretion occurred in the remainder. However, strong stimulation (> 4-fold) occurred only in 5 of the gsp-negative tumors. The basal phosphatidylinositol turnover rate was elevated in about 25% of gsp-negative somatotropinomas. These results demonstrate similar and highly variable effects of GHRH on both types of somatotropinoma, whereas the absence of gsp oncogenes is often associated with resistance to octreotide. The phosphatidylinositol turnover data suggest that defects within this second messenger system may be present in a subset of somatotropinomas without gsp oncogenes.
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