Screening Methods for Antihypertensive Drugs

Screening Methods for Antihypertensive Drugs

1. Definition, rationale & overview of antihypertensive screening

• Antihypertensive drug screening = the staged preclinical battery (in-vitro vascular/enzyme assays → in-vivo induced & genetic hypertension models → blood-pressure read-outs) used to detect, quantify and rank the blood-pressure-lowering activity of a candidate molecule before clinical testing (SK Gupta 4e Ch.16, pp.266–276; Vogel 4e Part I "Methods to Induce Experimental Hypertension", pp.135–157).
• Why animal models are needed: the aetiology of human essential (primary) hypertension is unknown and multifactorial, so no single model reproduces the human disease; models instead isolate one mechanistic driver (renal ischaemia, mineralocorticoid excess, sympathetic drive, genetic background, NO deficiency) to interrogate aetiology, pathophysiology, end-organ damage and treatment (SK Gupta 4e Ch.16, p.266).
• Cautionary principle (validity ceiling): extrapolation of findings from any experimental model to human hypertension requires a cautious approach — rat models "mainly share high blood pressure" but otherwise diverge widely in biochemistry, course and prognosis (SK Gupta 4e Ch.16, pp.266, 274–275).
• Hierarchy of a screening cascade (synthesised across sources):
  • Tier 1 — in-vitro / isolated tissue: vascular smooth-muscle (aortic-ring) relaxation, ACE inhibition, angiotensin-II antagonism, renin inhibition, endothelin antagonism — mechanism-defining, high-throughput, low animal cost (Vogel 4e Part I, pp.3–4, 107–109; SK Gupta 4e Ch.16, p.266).
  • Tier 2 — acute in-vivo functional: pithed rat, anaesthetised normotensive/ganglion-blocked rat, acute renal (Goldblatt) clip — fast pharmacodynamic confirmation (Vogel 4e Part I, pp.44–46, 136).
  • Tier 3 — chronic established hypertension: chronic renal (1K1C/2K2C), DOCA-salt, dietary, Ang-II-infusion, L-NAME, genetic SHR/Dahl — efficacy in a sustained hypertensive state with end-organ damage (SK Gupta 4e Ch.16, pp.268–273; Vogel 4e Part I, pp.137–157).
• Reference / standard antihypertensives used to validate screens (not the screen's targets): endralazine, nifedipine, urapidil (tail-cuff conscious-rat standards), captopril, enalapril, ramipril (ACE-inhibition standards), losartan / fonsartan (AT₁-antagonist standards) (Vogel 4e Part I, pp.49, 108, 150).
• Key endpoints across the cascade: % reduction in systolic/mean BP vs pre-drug control, duration of effect, ID₅₀/IC₅₀, potency ratio, pA₂/Schild slope (in-vitro antagonism), plasma renin activity (PRA), plasma/tissue angiotensin II, and end-organ measures (cardiac mass, proteinuria, glomerulosclerosis, endothelium-dependent relaxation) (SK Gupta 4e Ch.16, pp.267–273; Vogel 4e Part I, pp.4, 107–109, 140).