Binding and action of insulin-like growth factors and insulin in bovine luteal tissue during the oestrous cycle.
The effect of insulin-like growth factors (IGFs) and insulin on the release of progesterone and oxytocin from bovine corpus luteum was investigated at early (days 5-7), mid- (days 8-12) and late (days 15-18) luteal phases of the oestrous cycle in an in vitro microdialysis system. The expression of specific receptors was evaluated in bovine corpora lutea of the respective luteal stages. A 30 min infusion of IGF-1, IGF-2 (1.3, 13 and 130 nmol l-1) or insulin (13, 130 and 1300 nmol l-1) caused a stimulation of the release of progesterone (P < 0.05). IGF-1 was most effective in releasing progesterone. Oxytocin release from corpora lutea was stimulated by insulin at all doses tested (13-1300 nmol l-1), whereas the IGFs were only effective at the highest dose (130 nmol l-1) applied. The high doses of IGFs (130 nmol l-1) and insulin (1300 nmol l-1) stimulated the release of progesterone and oxytocin throughout the luteal phase (P < 0.05). For all three peptides, greatest stimulation was seen during the late luteal phase (days 15-18 of the oestrous cycle) with the peak of progesterone release directly related to peptide infusion (P < 0.05). In addition, IGF-1 stimulated total release of progesterone (units in 4 h) after the beginning of the stimulation during this phase (P < 0.05). IGF-1 caused a gradual increase of progesterone even beyond the time of peptide perfusion, whereas IGF-2 and insulin stimulated progesterone release only during the peptide perfusion. Distinct receptors for IGF-1 and IGF-2 were present in corpora lutea membrane preparations at all stages investigated. Specific binding for insulin was also seen in all stages of the cycle without any cycle-dependent changes in the amount of binding. The displacement of labelled insulin by unlabelled IGF-1 and IGF-2 did not show the rank of order that has been described as typical for insulin receptors (i.e. insulin > IGF-1 > IGF-2), but comparable binding affinities were observed for the three unlabelled ligands. Specific binding of IGF-2 was markedly higher than that of IGF-1 or insulin throughout the cycle (1.9- and 4.9-fold higher compared with IGF-1 and insulin, respectively). Receptor specificity did not change during luteal development. Binding affinity and capacity of IGF-1 receptor was constant throughout the oestrous cycle. Specific IGF-2 binding increased and showed a positive co-operativity towards the end of the cycle. Specific binding of insulin was not significantly different in the three luteal stages examined.
Sauerwein
H
H
Institut für Physiologie, Technische Universität München, Freising-Weihenstephan, Germany.
Miyamoto
A
A
Günther
J
J
Meyer
H H
HH
Schams
D
D
D000818:Animals; D002417:Cattle; D003338:Corpus Luteum / Q000187:drug effects / Q000378:metabolism*; D046508:Culture Techniques; D005260:Female; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology; D008183:Luteal Phase / Q000378:metabolism*; D010121:Oxytocin / Q000096:biosynthesis; D011374:Progesterone / Q000096:biosynthesis; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D017527:Receptor, IGF Type 2 / Q000378:metabolism; D011972:Receptor, Insulin / Q000378:metabolism; D013002:Somatomedins / Q000378:metabolism*; D013268:Stimulation, Chemical
D007328:Insulin; D017527:Receptor, IGF Type 2; D013002:Somatomedins; D011374:Progesterone; D010121:Oxytocin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin