Chronic Pressure-Natriuresis Relationship in Dogs with Essential Hypertension

A genetic model of essential hypertension in the dog was studied to describe the phenotypic expression of the arterial pressure, as well as to determine the relationship between mean arterial blood pressure (MAP), hormone, and renal excretory responses to four different levels of sodium intake (5, 40, 120, 240 mEq/day) delivered intravenously and isotonically. This model was developed at the University of Pennsylvania (U/Penn) and termed Pennsylvania hypertensive dogs (PHD). The MAP was recorded beat-by-beat, 24 h/day, in 16 dogs. Water and sodium balances were determined daily for 4 days at each level of intake and blood samples were collected on the last day of each salt step for analysis of plasma renin activity (PRA), atrial natriuretic peptide (ANP), aldosterone (ALDO), and vasopressin (AVP). After the study, the dogs were designated as hypertensive (PHD-HT) when the 24-h average MAP was greater than 110 mm Hg and systolic pressure was greater than 160 mm Hg. Dogs that failed to meet both criteria were designated as normotensive genetic controls (PHD-NT). Although sodium was retained during the first day of each increase of salt intake in both groups, a return to balance was observed within the 4 days. There was no apparent change in the slope of the chronic renal function curve in either group of PHD studied, although the PHD-HT exhibit a curve shifted to a higher level of MAP. Plasma hormone levels in both groups of PHD studied responded in a manner similar to normal mongrel dogs with reductions of PRA, ALDO, elevations of ANP, and no change in AVP. The young PHD-HT studied are similar in many ways to a subset of humans with essential hypertension, indicating a potential role for PHD in future studies of genetic hypertension

Concerted vs Stepwise Mechanisms in Dehydro-Diels–Alder Reactions

The Diels–Alder reaction is not limited to 1,3-dienes. Many cycloadditions of enynes and a smaller number of examples with 1,3-diynes have been reported. These “dehydro”-Diels–Alder cycloadditions are one class of dehydropericyclic reactions which have long been used to generate strained cyclic allenes and other novel structures. CCSD­(T)//M05-2X computational results are reported for the cycloadditions of vinylacetylene and butadiyne with ethylene and acetylene. Both concerted and stepwise diradical routes have been explored for each reaction, with location of relevant stationary points. Relative to 1,3-dienes, replacement of one double bond by a triple bond adds 6–6.5 kcal/mol to the activation barrier; a second triple bond adds 4.3–4.5 kcal/mol to the barrier. Product strain decreases the predicted exothermicity. In every case, a concerted reaction is favored energetically. The difference between concerted and stepwise reactions is 5.2–6.6 kcal/mol for enynes but diminishes to 0.5–2 kcal/mol for diynes. Experimental studies on intramolecular diyne + ene cycloadditions show two distinct reaction pathways, providing evidence for competing concerted and stepwise mechanisms. Diyne + yne cycloadditions connect with arynes and ethynyl-1,3-cyclobutadiene. This potential energy surface appears to be flat, with only a minute advantage for a concerted process; many diyne cycloadditions or aryne cycloreversions will proceed by a stepwise mechanism