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  • 1985-1989  (2)
  • Growth hormone  (1)
  • Nonlinear renewal theory  (1)
  • 1
    Electronic Resource
    Electronic Resource
    A mathematical analysis of small mammal populations (1987)
    Springer
    Journal of mathematical biology 25 (1987), S. 263-274 
    Details
    ISSN: 1432-1416
    Keywords: Population biology ; Nonlinear renewal theory ; Population waves: synchronization ; Rarefaction and compression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Populations of Microtus montanus, the montane vole, have been extensively studied. It is known that their reproductive activity is closely linked to the availability of the chemicals in growing plants. We use a mathematical model here to study how the length of the vegetative season and the natural reproduction rhythm of voles are involved in the long term dynamics of the population numbers. In particular, we use data obtained from Timpie Springs, Utah, and from Jackson Hole, Wyoming, to formulate a model. The novelty of this model is its use of littering curves that highlight the temporally discrete nature of vole reproduction. The model shows how the timing of the vegetative season can influence vole population sizes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00276436
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of acute and chronic insulin administration on insulin-like growth factor-I expression in the pituitary-intact and hypophysectomised rat (1989)
    Springer
    Diabetologia 32 (1989), S. 348-353 
    Details
    ISSN: 1432-0428
    Keywords: Growth hormone ; insulin ; insulin-like growth factor-I ; diabetes ; growth ; somatomedin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Although growth hormone is known to be the main regulator of insulin-like growth factor-I, insulin has also been shown to play a role in regulating serum insulin-like growth factor I levels in diabetic animals. While this effect is thought to be due to correction of metabolic perturbations, some studies have suggest that insulin may have a direct effect on growth and/or insulin-like growth factor-I levels. We have examined the effects of acute and chronic insulin administration to non-diabetic, pituitary-intact and hypophysectomised rats. Rats were injected intraperitoneally with insulin as an acute bolus (10 U) or a chronic subcutanious infusion (low dose; 2.4 U/day, high dose; 12 U/day) over 5 days. Insulin-like growth factor-I mRNA was quantitated by Northern and slot blots of RNA from various tissues. A small (less than 2-fold) but significant increase (p〈0.05) was seen in hepatic insulin-like growth factor-I mRNA abundance in pituitary-intact rats following acute insulin injection and chronic low dose insulin infusion. An increase in insulin-like growth factor-I mRNA levels was also seen in other tissues including diaphragm, lung, kidney and heart. A significant increase (p〈0.05) in serum insulin-like growth factor-I levels was also observed 6 h after insulin injection. In contrast, in pituitary-intact rats which received high dose insulin infusion and were hypoglycaemic at the time of death, tissue levels of insulin-like growth factor-I mRNA were reduced compared to saline-treated control groups. Similarly in the hypophysectomised rats neither acute nor chronic insulin administration had any consistent effect on insulin-like growth factor-I mRNA abundance in any of the tissues examined. This data suggests that insulin has no direct effect in regulating insulin-like growth factor-I gene expression. The small effects demonstrable in pituitary-intact rats may result from a synergistic action of insulin with growth hormone or other pituitary factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00277257
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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