Responses of glucose metabolism to insulin in perfused mammary tissue of lactating rats: influence of dietary history and recent insulin experience.
Mammary tissue of lactating rats has been perfused in situ to measure the effects of insulin and of previous dietary history on utilization of glucose and its incorporation into lipid. This experimental model allows the direct effects of insulin on mammary tissue to be characterized without influence from the secondary consequences of insulin administration that may accompany treatment of the intact animal with this hormone. In mammary tissue from rats starved for 24 h, glucose utilization was stimulated by insulin treatment. The threshold for insulin response was between 0.01 and 0.02 mU ml-1, and no further stimulation took place between 0.02 and 0.04 mU ml-1 insulin. The maximum response was reached within 50 min of the onset of insulin challenge and remained at a plateau value regardless of whether insulin was continuously present or was withdrawn after 15 min. Incorporation of glucose into lipid contributed to this glucose uptake. When no insulin was present in the perfusate, the rate of this process was around 3-fold greater in perfused mammary tissue from fed lactating rats than from those starved for 24 h. Insulin accelerated lipogenesis from glucose approximately 3- and 2-fold, respectively, in these two experimental groups. As for glucose uptake, the role of insulin in the regulation of mammary lipogenesis appeared to be to 'prime' the tissue and commit it to a response that was subsequently insulin independent.
Calvert
D T
DT
Hannah Research Institute, Ayr, UK.
Clegg
R A
RA
D000818:Animals; D004032:Diet; D005260:Female; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D007774:Lactation; D008055:Lipids / Q000096:biosynthesis; D008321:Mammary Glands, Animal / Q000187:drug effects* / Q000378:metabolism*; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar; D013217:Starvation / Q000378:metabolism
D007328:Insulin; D008055:Lipids; D005947:Glucose