Tritium labelling of two highly selective agonists for CCK‐B receptor: [3H]propionyl‐Tyr(SO3Na)‐gNle‐mGly‐Trp‐(N‐Me)Nle‐Asp‐Phe‐NH2([3H]pBC 264) [3H]propionyl‐γDLys‐Trp‐Nle‐Asp‐Phe‐NH2([3H]pBC 254)