Insulin potentiates expression of myocardial heat shock protein 70

Since insulin stimulates nitric oxide (NO) production and an increase in NO following heat shock is required for myocardial heat shock protein 70 (Hsp70) synthesis, we hypothesized that insulin would enhance myocardial Hsp70 synthesis by augmenting NO signaling. We examined whether a physiologic dose of insulin increased myocardial Hsp70 in unstressed and heat shock treated rats.

Adult male Sprague-Dawley rats were assigned to groups: (1) control, (2) insulin injected (200 microU/gm body weight), (3) heat shock treated (core body temperature 42 degrees C for 15 min), (4) heat shock and insulin treated, (5) L-nitroarginine methyl ester (L-NAME) and heat shock and insulin treated, (6) sodium nitroprusside (SNP) and heat shock and insulin treated. Six hours later, myocardial Hsp70 content and localization was analyzed.

Hsp70 was increased in heat shock treated hearts (120.6+/-16.8 ng/mg protein, P < 0.001) vs. control (12.9+/-2.0 ng/mg protein), or insulin treated hearts (15.5+/-0.83 ng/mg protein). In addition, Hsp70 was increased in the heat shock and insulin treated hearts (164.4+/-7.53 ng/mg protein) compared to control, insulin only (P = 0.001) or heat shock only treated hearts (P = 0.01). L-NAME did not abolish the insulin induced increase in Hsp70 in heat shocked hearts (195.2+/-13.4 ng/mg protein, P = 0.21) and SNP did not further enhance Hsp70 in the insulin and heat shocked group (188.9+/-8.2 ng/mg protein, P = 0.71). Western analysis and confocal microscopy revealed a lowlevel expression of myocardial Hsp70 in response to insulin. Hsp70 was localized primarily in blood vessels after insulin or heat shock treatments.

Insulin caused a low-level expression of myocardial Hsp70 and potentiated Hsp70 synthesis in response to heat shock. The ability of insulin to potentiate Hsp70 after heat shock is independent of NO signaling as it was not altered by either LNAME or SNP pretreatment. Blood vessels appear to be the primary site of Hsp70 after insulin or heat shock treatment.