Structural requirements of the oxytocin receptor in rat uterus

Published and newly calculated pA₂-values of 147 neurohypophyseal hormone analogues (7 positions varied) acting as inhibitors of oxytocin on isolated rat uterus in vitro have been subjected to fractionation according to the method by Free and Wilson which was slightly modified for this purpose. The computation was carried out in several steps. After each step, substances with outlying pA₂ -values were el minated. The reduced group containing 73–79% of the original substances displayed a high degree of additivity of side chain contributions (SCC). This group seems to follow the “participation” rule as formulated by Free and Wilson. Analysis of the group of eliminated substances and of the resulting SCC-spectrum (level diagram) enabled us to draw some conclusions concerning the structural requirements of receptor binding: i) The intact ring structure is necessary for the peptide-receptor interaction: linear peptides or peptides with an extended ring are always outliers; ii) Carba analogues (substitution with CH₂ in the disulfide ring) display better affinities than peptides with an S-S ring; d -Arg⁸ substitution decreases the binding affinity; iii) Considerably better additivity is achieved when peptides are divided into subgroups with vasopressin-like and oxytocin-like features; populations of receptors more specific for vasopressin and for oxytocin, respectively, can be assumed. Estimates of the “true” receptor-peptide dissociation constants can be obtained by summation of the corresponding SCC's in each investigated position. The value obtained for oxytocin is identical with the medium affinity binding site on myometrial cells, and not with the high affinity site. A nonlinear relationship exists between SCC's computed from pA₂-values for magnesium-free and magnesium-containing (0.5 mm ) media but no evidence speaks in favor of a Mg-potentiating effect on receptor binding.     

Does preoperative needle localization lead to an increase in local breast cancer recurrence?

Between 1978 and 1981, 74 women with nonpalpable breast cancer underwent surgery after localization guides were placed. In 72 patients, guides were introduced parallel to the chest wall; in two the needle was positioned anteroposteriorly under computed tomographic guidance. Fifty-six cases (76%) were infiltrating cancer; 13 (17%), intraductal cancers; two (3%), inflammatory; and three (4%), lobular carcinoma in situ. Surgery was not used to treat the latter five patients. In the remaining 69 women, 42 (61%) were treated by means of modified radical mastectomy; six (9%), total mastectomy; 12 (17%), local excision and radiation therapy; and seven (10%), local excision alone; exact therapy for two women (3%) was unknown. At a minimum follow-up of 5 years, none of the 67 women in whom the parallel approach was used had a local recurrence. The authors conclude that preoperative placement of guides parallel to the chest wall does not appear to increase the risk of local breast cancer recurrence.     

Inhibition of heparin activity in plasma by soluble fibrin: evidence for ternary thrombin-fibrin-heparin complex formation

The ability of heparin to dramatically enhance the inactivation of thrombin (IIa) by antithrombin III (ATIII) in buffer is negated through formation of a IIa-fibrin-heparin ternary complex (Hogg and Jackson, Proc Natl Acad Sci USA 86:3619, 1989; Hogg and Jackson, J Biol Chem 265:241, 1990). IIa, in this ternary complex, is protected from inactivation by ATIII. Our aim was to determine whether fibrin also compromises heparin efficacy in plasma. We found that soluble fibrin ablated the heparin-mediated prolongation of the thrombin time with half-maximal effect at 60 nmol/L fibrin. The heparin-mediated prolongation of the activated partial thromboplastin time (APTT) was also reduced by fibrin with half-maximal effects at 140 nmol/L fibrin using 0.12 U/mL heparin and 500 nmol/L fibrin using 0.25 U/mL heparin. The mechanism of inhibition of heparin activity by fibrin in plasma was determined by measuring IIa-ATIII complexes by enzyme-linked immunosorbent assay (ELISA). Fibrin was found to inhibit the heparin- catalyzed inactivation of IIa by ATIII with half-maximal effect at 97 +/- 19 nmol/L fibrin. Fibrin had no effect on the heparin-catalyzed inactivation of factor Xa by ATIII in plasma, using either standard heparin, a heparinoid preparation (Orgaran; Organon, Lane Cove, Sydney, Australia), or low-molecular weight heparin. These findings imply that fibrin is a potent modulator of heparin activity in vivo by inhibiting heparin-catalyzed IIa-ATIII complex formation through formation of ternary IIa-fibrin-heparin complexes.     

Postmitotic marrow neutrophils and neutrophil mobilization in man: role of the spleen

The relationship between postmitotic marrow neutrophils (PMMN) and neutrophil increment in blood after an intravenous dose of 3 mg hydrocortisone/kg was studied in patients with normal-sized spleens and compared with splenectomized and splenomegalic patients. PMMN were quantified from the ferrokinetic measurement of the normoblast number and the PMMN/normoblast ratio in bone marrow biopsy sections. In 12 control patients with normal PMMN the increment was 3.50 +/- 1.13 X 10(9) neutrophils/liter. An excellent correlation was found between the number of PMMN and the maximal neutrophil increment (y = 826x - 1021, r = 0.93, p less than 0.001) among 24 patients with normal spleen size and a wide range of marrow cellularity. Significantly higher responses were observed in 10 splenectomized patients (y = 872x + 1429, r = 0.92, p less than 0.001). The two regression lines were shown to be parallel, indicating a diminution of the response by 2.5 X 10(9) neutrophils/liter in the presence of a normal spleen. In 11 hypersplenic patients the responses were further reduced and more variable. Peak neutrophilia occurred after median values of 2, 3, and 4 hr in the hypersplenic, the control, and the splenectomized group, respectively. These studies indicate that allowing for the different response curves neutrophil increments may be used as an index of PMMN in patients with normal spleen size and in splenectomized patients. They further suggest sequestration of the prematurely released cells by the spleen.