Modulation of the affinity of the vasopressin receptor by magnesium ions.

The binding of [3H]vasopressin (AVP) and the 125I-labelled vasopressin antagonist (VP-AT) d(CH2)5[Tyr2(Me),Tyr9(NH2)]AVP to rat liver membranes was examined with or without the addition of milimolar concentrations of divalent cations. The binding of vasopressin was enhanced by Mg2+ and Co2+ and markedly decreased by EGTA. The addition of EGTA and Mg2+ together restored the binding to a value similar to that of Mg2+ alone. On the contrary, the addition of Mg2+, Co2+, EGTA, and the combination of EGTA and Mg2+ decreased the binding of VP-AT to rat liver membranes. Kinetic analyses showed that Mg2+ increased the Kd twofold for VP-AT; that is from 0.13 nM to 0.28 nM. Moreover, it showed that the receptor with or without the addition of Mg2+ consists of a single population of binding sites, indicating that the receptor is switched from a high affinity to a low affinity state for VP-AT in the presence of 10 mM Mg2+. GTP gamma S was unable to block the effect of Mg2+ on the binding of VP-AT. These results suggest that this divalent cation interacts with receptor itself producing a conformational changes which thus modulates the affinity of the receptor.     

A NEW SPECIES OF BEAKED WHALE MESOPLODON PERUVIANUS SP. N. (CETACEA: ZIPHIIDAE) FROM PERU

Mesoplodon peruvianus , a new species of beaked whale, is described on the basis of ten specimens which have either stranded or been captured between 11°12'S and 15°19'S latitude along the coasts of the provinces of Lima and Ica, south central Peru. This is the thirteenth living species of Mesoplodon recognized in the world's oceans. The animals that were examined were uniformly gray above, shading to lighter gray below. This whale is the smallest species of Mesoplodon (maximum body length 3.72 m) and is characterized by its teeth, which are small (31 to 65 mm long), ovate in cross section, and positioned 2.5% to 8.4% of the mandibular length from the anterior extremity, and posterior to the mandibular symphysis.     

幼年大鼠诱发排卵条件下卵巢前列腺素(PGs)的含量变化及其生理作用

本实验用幼年大鼠经PMSG/hCG诱发排卵,研究了印巢PGE_2、PGF_(2α) 、6-酮-PGF_(1α) 及TXB_2在排卵过程中的变化。实验表明卵巢PGE_2、PGF_(2α) 及6-酮-PGF_(1α) 在排卵前达到峰值,在排卵后,均趋下降。TXB_2未出现明显变化。受试动物经消炎痛处理后,不仅使排卵受到严重抑制,而对上述三种PGs在排卵前的上升也表现了显著的抑制。提示在卵泡破裂过程中PGs的重要调节作用,PGE_2、PGF_(2α)均可能参与排卵,其中尤以PGE_2的作用最为显著。     

Populations of the spinach wilt pathogen, Fusarium oxysporum f. sp. spinaciae, in the root tissues, rhizosphere, and soil in the field.

Populations of Fusarium oxysporum f. sp. spinaciae in root tissues and rhizosphere soil of diseased spinach plants were higher than in the root tissues and rhizosphere soil of healthy plants. Populations in soil rhizosphere were higher than in nonrhizosphere soil. The fungus populations were very low in the root tissues of the nonsusceptible strawberry, broccoli, chinese cabbage, and mustard grown in the infested field. The populations were low at the beginning of the season, increased, and remained high during the summer, then dropped in the fall. The fungus populations ranged from 1600 to 2600 propagules/g in the top 10 cm of soil, declined sharply between 11 and 20 cm, and were nondetectable between 41 and 60 cm.