Mitogenic action of osteogenic growth peptide (OGP): role of amino and carboxy-terminal regions and charge

We have recently reported the discovery of a 14-amino-acid osteogenic growth peptide (OGP). In vivo OGP increases bone formation and trabecular bone density. Physiologically it is found in serum complexed to an OGP binding protein (OGPBP). In vitro OGP has a biphasic effect on osteoblastic MC 3T3 E1 and fibroblastic NIH 3T3 cell proliferation; at low concentrations (0.01-1.0 and 1.0-100.0 pM, respectively) it is highly stimulatory with an inhibition at higher doses. To assess possibilities of labeling synthetic OGP to obtain radio- or fluorescent ligands, OGP analogues were extended at the N- or C-termini with Cys or Cys(S-NEtSucc) or the OGP Tyr-10 replaced by 3-I(Tyr). All analogues with N-terminal modifications, as well as the [Cys15]OGP-NH2 retained the OGP-like dose-dependent effect on proliferation of the MC 3T3 E1 and NIH 3T3 cells, although the magnitude of stimulation was lower, approx. 2/3 that of the native-like synthetic OGP. The [Cys15(S-NEtSucc)]OGP-NH2 and [3-I(Tyr10)]OGP shared only the inhibitory activity of OGP. This suppression is further shared by a number of other positively and negatively net charged, but not net neutral, peptides. Both N-terminal-modified analogues displayed a decreased binding activity to the OGPBP. All analogues except reverse OGP, [3-I(Tyr10)]OGP and [Cys15(S-NEtSucc)]OGP-NH2 reacted with anti-OGP antibodies. These data are not only important for labeling purposes but suggest a respective role for the OGP N-and C-terminal regions in binding to the OGPBP and putative OGP receptor. It appears that the OGP proliferative activity represents the net effect of stimulation specific to the OGP structure and nonspecific inhibition associated with the peptide's high positive net charge.

Biological activities of angiotensin II-(1-6)-hexapeptide and angiotensin II-(1-7)-heptapeptide in man

Biological activities of angiotensin II-(1-6)-hexapeptide [ANG-(1-6)] and angiotensin II-(1-7)-heptapeptide [ANG-(1-7)] were studied in 5 normal men and 3 patients with Bartter's syndrome. The angiotensins were infused iv in each subject from 0900 h to 0915 h at a rate of 21 nmol(16.8 micrograms)/kg X min and 18 nmol(16.2 micrograms)/kg X min for ANG-(1-6) and ANG-(1-7), respectively. In the normal men a significant rise in blood pressure was observed by the infusions of both peptides. Average increments of blood pressure for ANG-(1-6) were 17/14, 23/18, 22/15 and 17/14 mmHg at 2, 5, 10 and 15 min, respectively, and those for ANG-(1-7) were 19/15, 20/17, 13/13 and 15/13 mmHg at 2, 5, 10 and 15 min, respectively. The duration of pressor actions after the cessation of the infusions (T) was 10 min for ANG-(1-6) and 20 (for systolic) and 30 (for diastolic) min for ANG-(1-7). T for ANG-(1-6) was shorter than and T for ANG-(1-7) was similar to T for Ile5-angiotensin II (Ile5-ANG II) reported previously in 7 normal men 5 of whom were the same as examined in the present study. On the other hand, both peptides did not cause a rise in blood pressure in the 3 patients with Bartter's syndrome. Both angiotensins did not cause an increase in plasma aldosterone but did cause a significant decrease in plasma renin activity both in the normal men and in the patients. From these results and our previous observations of inactivity of angiotensin II-(5-8)-tetrapeptide, a pressor action of angiotensin II-(4-8)-pentapeptide, and pressor, renin-suppressing and steroidogenic actions of angiotensin II-(3-8)-hexapeptide in normal men, it is thought that ANG-(1-6) and ANG-(1-7) are bound to angiotensin II (ANG II) receptor in the peripheral arterioles and show pressor actions (less than 0.024% and less than 0.028% of Ile5-ANG II, respectively) and suppress renin mainly via short loop feedback and that the shortest biologically active ANG II molecules for pressor, renin-suppressing and steroidogenic actions are Tyr-Ile-His, Val-Tyr-Ile-His and Val-Tyr-Ile-His-Pro-Phe, respectively, in man. It is also evident that ANG-(1-6) is more rapidly metabolized than ANG-(1-7) or Ile5-ANG II in man.

Angiotensin receptors in vascular tissue

The biologic effect of angiotensin II is triggered by its interaction with components of target organs, which specifically recognize the hormone. These receptors have been studied with the use of radioactive angiotensin and, as for other peptidic hormones, have been localized in the plasma membrane of target cells. Such angiotensin receptors have been characterized in three target organs: vascular tissue, uterus and adrenal cortex. The binding characteristics differ in contractile tissue and in adrenal glands, the N and C terminal ends of angiotensin being involved in the former, whereas the N terminus does not appear to have the same importance in the latter. Numerous factors, including ionic composition, seem to be able to modify angiotensin-receptor interaction in vascular smooth muscle. However, the molecular mechanisms responsible for angiotensin binding and for the transmission of the signal determined by receptor-angiotensin interaction are not yet understood. As observed with other peptidic hormones, the number of angiotensin receptors seems to be susceptible to variation under certain conditions. In uterine smooth muscle, it was shown that the number of receptors increased after nephrectomy, a phenomenon which was prevented by the prolonged infusion of angiotensin. The significance of such a variation remains unknown, but it may be partially responsible for the inverse relationship that exists between the endogenous angiotensin level and the pressor effect of exogenous angiotensin. In the near future, investigation of the angiotensin-receptor mechanism will probably answer whether the variation in angiotensin receptors is similar in all target tissues and whether an angiotensin-receptor mechanism is involved in the pathogenesis of certain varieties of hypertension. In addition, a precise understanding of the angiotensin-receptor interaction with help the development of new angiotensin antagonists.

Degradation of angiotensin II by plasmin

1. Synthetic angiotensin II (Hypertensin, Ciba, Basel) was incubated with a water-insoluble preparation of plasmin (E.C. 3.4.4.14) and the resulting products analysed by paper chromatography and N-terminal amino-acid analysis.2. Only the N-terminal asparagine was split off from the peptide. This indicates that plasmin attacks the Asn-Arg but not the Arg-Val in angiotensin II molecule.

Chemistry of Synthetic Angiotensin

A short review is given of the development of synthetic angiotensin. Also discussed are enzymic experiments, showing that production of the synthetic substance leads to valyl-5-angiotensin-II, in which all amino acids are completely in the l -configuration. Small amounts of diastereoisomers in intermediates, like l -valyl- d -tyrosyl- l -valyl- l -histidyl- l -prolyl- l -phenylalanine which was isolated and identified, are completely eliminated during the synthetic process. Valyl-5-angiotensin II-aspartyl-β-amides are very slowly hydrolyzed in aqueous solution to valyl-5-angriotensin II and a small amount of the heptapeptide, H·Arg-Val-Tyr-Val-His-Pro-Phe·OH, with negligible decrease in pressure activity of the solution.